Main article: Phineas FlynnPhineas Flynn (voiced by Vincent Martella) Like other characters, his age is not mentioned. Phineas, along with his stepbrother Ferb Fletcher, star in the A-Plot of every episode. The series concerns Phineas's attempts to avoid boredom by finding something new to do every day of the summer vacation. He does this with his less-talkative stepbrother Ferb, and often with many other neighborhood children. He is known to be very selfless and energetic.
Phineas comes from a blended family. The creators chose this arrangement because they considered it underused in children's programming as well as from Marsh's experiences in one. As a character, Phineas has received a positive critical response, with one reviewer describing him and his brother as a "comical pairing." Phineas appears in Phineas and Ferb merchandise, including plush toys, t-shirts, and a video game.
Main article: Ferb FletcherFerb Fletcher (voiced by Thomas Sangster) is Phineas's intelligent but laconic stepbrother from England and created by Phineas and Ferb co-founders Dan Povenmire and Jeff "Swampy" Marsh. He first appeared in the show's pilot episode, "Rollercoaster."
Ferb and his stepbrother Phineas Flynn spend their days during their summer vacation having fun. They are featured in every episode's A-Plot constructing large scale inventions or taking part in other outlandish activities. Ferb, an engineering genius, allows Phineas to do most of the talking for the pair and is described as "more of a man of action," by Phineas, which makes him more of a plot device than a developed character. Ferb is more likely to sing than speak, but most often has a one-liner in the episode. Ferb is named after a friend of the show's creators who was an expert on tools and, at times, stayed rather silent.
Main article: Candace FlynnCandace Flynn, (voiced by Ashley Tisdale) is Phineas's fifteen-year-old older sister and Ferb's stepsister. She first appeared in the pilot episode along with the other main characters who star in the A-Plot. Candace does not approve of the inventions her brothers create and during each episode attempts to "bust her brothers" by showing their mom. Her best friend is Stacy Hirano and also has an obvious crush on a boy named Jeremy Johnson but is very oblivious to the fact he likes her back. She comes from a reconstituted family, selecting this arrangement because the series's creators considered it underused in children's programming as well as Marsh's past experiences in one. As a character, she has received a positive critical acclaim, having appeared in other media such as video games.
Perry the Platypus
Main article: Perry the PlatypusPerry the Platypus (vocal effects by Dee Bradley Baker), A.K.A. Agent P, is Phineas and Ferb's pet platypus and first appeared along with a large portion of the main cast in the pilot episode "Rollercoaster." Perry is featured as the star of the B-Plot for all but one episode of the series alongside his arch-nemesis Dr. Heinz Doofenshmirtz. He is a primarily silent character, with the only noises being the occasional rattling of his bill. Perry is often referred to, incorrectly, by Ferb as "the only mammal that lays eggs."
Main article: Dr. Heinz DoofenshmirtzDr. Heinz Doofenshmirtz (voiced by Dan Povenmire) is a mad scientist appearing in all but one episode's B-Plots thus far. He is the father to teenage Vanessa Doofenshmirtz and is the head of his own company, Doofenshmirtz Evil Inc. Depending on the episode, Dr. Doofenshmirtz's main goal is to either destroy or rule the Tri-State Area which was suggested to him as a starting point before trying to take over the world. Routinely bumbling, incompetent, and forgetful, Doofenshmirtz's plans–always involving various gadgets and inventions–have been thwarted by Perry the Platypus. After most defeats, he shouts his catchphrase, "Curse you, Perry the Platypus!" His first invention as a child was simply called "Inator" which led to his modern contraptions usually ending with the suffix of the same name.
Throughout the series, Doofenshmirtz's flashbacks (of which are often told after Perry has been captured) explore his mentally abusive and lonely childhood growing up in the fictional village Gimmelshtump, Druelselstein. Before becoming an evil scientist, Doofenshmirtz was a bratwurst vender until being put out of business by the hot dog industry. Doofenshmirtz usually monologues and displays acts of cartoon-style physical violence towards his nemesis Perry, a skilled anthropomorphic platypus secret agent. Doofenshmirtz appears in several merchandise pieces, particularly the book series, and the video game.
Baljeet (voiced by Maulik Pancholy) is Phineas' and Ferb's friend and neighbor. A shy and polite boy of Indian descent, he often helps the boys with their ideas and displays his knowledge of algebra and trivia. He also has a compulsive need to get good grades. Unlike many characters, his last name hasn't been revealed.
Carl the Intern
Carl the Intern (Tyler Alexander Mann) is Major Monogram's young intern in charge of video taping Monogram when he is being inter viewed. He is a bit careless, wears glasses, and sometimes forgets to focus the camera correctly.
The Fireside Girls symbol, first shown in the episode "Isabella and the Temple of Sap."The Fireside Girls are a group of ten girl scout-like girls led by Isabella in troop 46231. Isabella and the other Fireside Girls usually help Phineas and Ferb in their projects which, in turn, are at times created to help the Fireside Girls with a humanitarian cause.
Other members of the troop:
- Gretchen (voiced by Ariel Winter) wears glasses and has short auburn hair. She is second in command in the troop and the first (besides Isabella) member of the troop who had been addresed by name.
- Holly (voiced by Cymphonique Miller)
- Katie (voiced by Isabella Acres)
- Milly (voiced by Isabella Murad)
- Adyson Sweetwater (voiced by Madison Pettis) The second Member of the troop to be addressed by name, and the first to have been given a last name as well.
- Ginger (voiced by Tiffany Espensen)
Lawrence Fletcher (voiced by Richard O'Brien) is the father of Ferb and stepfather of Phineas and Candace. Lawrence is an archaeologist from England and is portrayed like a sitcom dad as being scatterbrained and unaware of what is going on. He agrees to follow Phineas's instructions and even forces Candace to cooperate as if he considers Phineas and Ferb's skills normal. Unlike the boys' mother, he has seen some of the boys' inventions with no negative assumptions believing that their mother approves. Jeff "Swampy" Marsh has said that Lawrence Fletcher is very similar to his stepfather, Bill.
Linda Flynn-Fletcher (voiced by Caroline Rhea) is the mother of Phineas and Candace and stepmother to Ferb. Unaware of the large-scale projects that Phineas and Ferb create on a daily basis, Candace often drags her away from other interests in an attempt to get the boys in trouble. Each creation is somehow destroyed or eliminated moments before "Mom" arrives leaving Candace dumbfounded and Linda once more reluctant to believe Candace the next time. She was also a one-hit wonder known as "Lindana" with her song, "I'm Lindana and I Wanna Have Fun" which is used as elevator music throughout the series. She is based on Dan Povenmire's sister, also named Linda.
Isabella Garcia-Shapiro (voiced by Alyson Stoner) is a Jewish Mexican girl. She is one of the brothers' best friends and has an obvious crush on Phineas Flynn of which he is unaware, though he has shown he cares for her from time to time. She is known for the catchphrase, "Whatcha doin'?" and is the leader of the Fireside Girls troop 46231. The troop often helps Phineas and Ferb in their projects. She is named after series creator Dan Povenmire's oldest daughter.
Stacy Hirano (voiced by Kelly Hu) is Candace's best friend. She has relatives that live in Japan. Stacy is shown to be annoyed by Candace's constant attempts to bust Phineas and Ferb, and would prefer to just have fun with the inventions.
Jeremy Johnson (voiced by Mitchel Musso) is Candace's crush and later boyfriend. His age, like most other characters, is unconfirmed, but he appears to be about the same age as Candace. He works at Mr. Slushy Burger (sometimes named Mr. Slushy Dawg). In "Summer Belongs to You," it was confirmed that he and Candace had become boyfriend and girlfriend; toward the end of the episode, they kissed. He also has a band called "The Incidentals."
Major Francis Monogram (voiced by Jeff "Swampy" Marsh) is the head of the O.W.C.A. (Organization Without a Cool Acronym) Department and Perry the Platypus' boss. He usually appears on a giant screen giving Perry instructions for his next mission to stop Dr. Heinz Doofenshmirtz's endless attempts to take over the Tri-State Area. His uniform prominently features the initials "MM." He has a monobrow and wears a toupée. Just like Doofenshmirtz, he has appeared in every episode of the series to date except, "Isabella and the Temple of Sap."
Buford van Stomm
Buford van Stomm (voiced by Bobby Gaylor) is frequently referred to as someone of which everybody is afraid, but he rarely hurts anyone on-screen. He is portrayed as a nice person with a tough guy attitude more often than as a bully. Phineas believes that Buford only bullies out of boredom thus Phineas often invites him to keep his mind occupied. He is thought not to get along with Baljeet, but in most episodes it is shown that they share a friendly bond.
Vanessa Doofenshmirtz (voiced by Olivia Olson) is Heinz and Charlene Doofenshmirtz's daughter. She is sarcastic, mild-mannered, cynical, and dresses in a goth style. Vanessa is aware that her father is a mad scientist and knows about her father's nemesis, Perry the Platypus. She is often exasperated by her father whenever he tries to establish a "father-daughter" bond between them as he doesn't really understand her interests and often assumes that she is also interested in "evil." She often tries to convince her mom that her dad is an "evil mad scientist" but, much like Candace, ultimately always fails when she does appear trying to catch him in the act. She does, however, occasionally show appreciation for what he does for her, as he is clearly dedicated to her and he taught her how to drive. Although Ferb has a crush on her, she remains oblivious to his affections as she already has a punk (not visigoth) boyfriend named "Johnny."
Vivian Garcia-Shapiro (voiced by Eileen Galindo), or simply "Viv," is Isabella's mother and lives across the street from Phineas and Ferb. She is a Jewish Mexican, one of Linda's best friends, and plays upright bass in a jazz band with Linda Flynn and Jeremy's mom. She is known for talking very fast and often making useless comments such as, "Oh, Candace, look how tall you've gotten." despite seeing Candace only a week earlier.
Pinky (vocals by Dee Bradley Baker) is Isabella's pet chihuahua. Much like Perry the Platypus, Pinky also lives a double-life as a secret agent for the O.W.C.A. under the codename, "Agent P" in a division run by a commander named Wanda. Pinky's nemesis is Professor Poofenplotz. Although he does not like dog food, Pinky will eat just about anything–especially his favorite; grilled cheese sandwiches, and even inedible objects, having once swallowed Isabella's Fireside Girl sash. Pinky always shakes as an ongoing joke about the behavior of Chihuahuas. He first appeared in the episode, "Journey to the Center of Candace."
Norm (voiced by John Viener) was created by Dr. Doofenshmirtz to destroy Perry the Platypus. Introduced in "Greece Lightning," he is a giant robotic mild-mannered businessman who often says, "The enemy of platypus is man." Norm has appeared in other episodes. For instance, in the episode, "Traffic Cam Caper," Perry borrows Norm as a ride to steal the traffic cam disk, for it has evidence that Perry is a secret agent. He was once a part of the O.W.C.A. but was fired because he was not an animal.
Charlene Doofenshmirtz (voiced by Allison Janney) is the former wife of Dr. Heinz Doofenshmirtz and shares custody of their daughter, Vanessa. Unaware of Dr. Doofenshmirtz's "evil" side, and in fact saying she does not believe someone can ever be truly evil, she divorced him due to a lack of common interests and having different life-goals. She is often called by Vanessa who tries to "bust" her father but to no avail. Charlene and Linda Flynn-Fletcher are often paired up in a cooking class owned by Chef Pierre and in "I Scream, You Scream" were distracted by both Candace and Vanessa at the same time. She still goes to Doofenshmirtz family reunions claiming that she "kept the name," as seen in "Thaddeus and Thor."
Suzy Johnson (voiced by Kari Wahlgren), known as Little Suzy Johnson, is Jeremy's little sister. She has a high-pitched squeaky voice and appears very sweet and innocent. However, she is actually very spoiled and manipulative and very possessive over Jeremy, once saying to Candace, "There is only one girl in Jeremy's life" and thus will do anything to keep Candace away from her brother.
Grandpa Clyde and Grandma Betty Jo
Grandpa Clyde Flynn and Grandma Betty Jo Flynn (voiced by Barry Bostwick and Caroline Rhea respectively) are Linda's parents, Phineas and Candace's maternal grandparents and Ferb's step-grandparents. Every summer, they invite the family along with many neighborhood kids to a lakehouse which Phineas calls, "Camp P&F". Though they are old, they often participate in the kids' capers. Grandpa Clyde, like Phineas and Ferb, has a great sense of mechanics, as seen in "Crack That Whip!" Betty Jo is also shown in the same episode to have a fierce rivalry with Edna Hildagard, Jeremy and Suzy's grandmother.
Grandpa Reginald and Grandma Winifred
Grandma Winifred Fletcher and Grandpa Reginald Fletcher (voiced by Malcolm McDowell and Jane Carr) are Ferb's grandparents and Lawrence Fletcher's parents that live in England. Known alternatively as the "Flying Fishmonger," Grandpa Reginald was a daredevil 40 years ago, driving a fish-shaped motorcycle called "The Holy Mackerel" and having an "anthem" so dreary that it made rain.
Roger Doofenshmirtz (voiced by John O'Hurley) is mayor of Danville and Dr. Heinz Doofenshmirtz's younger brother. Heinz often states angrily that Roger is their mother's favorite son. In "Tree to Get Ready" Roger states that he is, "the most handsome and charming man in the Tri-State area."
Irving (voiced by Jack McBrayer) is Phineas' and Ferb's self-proclaimed biggest fan. He always carries a scrapbook that he filled with images and souvenirs from Phineas and Ferb's big ideas as well as a strand of Ferb's hair. Irving has an older brother Albert, who is self-nicknamed 'The Truth Detector.'
Django Brown (voiced by Alec Holden) is a friend of Phineas and Ferb. Django is the son of the artist Beppo Brown from "Oil on Candace," who is famous for his work in making giant creations, from refrigerators to dental floss. He is named after co-creator's Jeff "Swampy" Marsh son, Django Marsh, who voices minor characters on the show. 
Love Händel is a rock band idolized by many in the Danville Tri-State Area, first seen the episode, "Dude, We're Gettin' the Band Back Together!" Lawrence Fletcher and Linda Flynn shared their first kiss at a Love Händel concert. Shortly afterward, plagued by infighting caused by the pressures of a dwindling fanbase, Love Händel split up. Lead Singer Danny (voiced by Jaret Reddick) became the owner of Danny's Music Shop. Bass Player Bobbi Fabulous (voiced by Carlos Alazraqui) became the owner of Bobbi's Fashion Salon and Linda's hairdresser. Sherman "Swampy" (voiced by Steve Zahn) ended up working at the Danville Public Library believing he had lost of rhythm. Eventually all three members are convinced to reunite for a concert in the Flynn/Fletcher's backyard, in which they sing their hit song, "You Snuck Your Way Right into My Heart." Love Handel occasionally reappears in other episodes where they sing their songs.
Dr. Hirano (voiced by Ming Wen) is Stacy's mother. She removed Isabella's tonsils in, "I Scream, You Scream." She is often referred to through conversations between Candace and Stacy where Candace gratifies, "Stacy, you're a genius!" and Stacy replies, "Could you call my mom and tell her that?"
There are several characters that reappear as recurring joke such as farmer and wife. The wife always tells her husband "I can't believe you (blank) without getting a (blank)" and then it falls from the sky and sometimes hits her. For example, "I can't believe you bought a bunny farm but forgot to buy any bunnies!" A pack of rabbits then falls from the sky and hits her. Another one is the Giant Baby Head. In an interview, Dan Povenmire stated that the head had originated from a storyboard panel that writer Mike Diederich had drawn which director Rob Hughes found hilarious enough to create an entire bit around. It appears in One Good Scare Ought to Do It!, "It's a Mud, Mud, Mud, Mud World", "Chez Platypus", "The Bully Code", "The Wizard of Odd", and "We Call It Maze." 
Dr. Doofenshmirtz's mother (Cloris Leachman) has appeared. She refers to Roger being her favorite child and often ignores Heinz. Albert (voiced by Diedrich Bader), Irving's Brother has appeared in "Not Phineas and Ferb", "The Doof Side of the Moon", and "Nerds of a Feather".
Celebrity Guest Stars
- Evander Holyfield as himself in the episode, "Raging Bully"
- Billy Ray Cyrus as Buck Buckerson in the episode, "It's A Mud, Mud, Mud, Mud World"
- Clancy Brown as The Drill Sergeant in the episode, "Phineas And Ferb Get Busted"
- Geraldo Rivera as Morty Williams in the episode, "Phineas and Ferb Get Busted"
- Brenda Song as Slushie Dawg Competetor in the episode, "Unfair Science Fair"
- David Mitchell as Mitch in the episode, "The Chronicles Of Meap"
- Lorenzo Lamas as Meap in the episode, "The Chronicles Of Meap"
- Corbin Bleu as Coltran in the episode, "The Baljeatles"
- Jennifer Stone as Amanda in the episode, "Phineas and Ferb's Quantum Boogaloo"
- Moises Arias as Fred in the episode, "Phineas and Ferb's Quantum Boogaloo"
- Noah Munck as Xavier in the episode, "Phineas and Ferb's Quantum Boogaloo"
- Big Bad Voodoo Daddy as themselves in the episode, "Phineas Ferb's Christmas Vacation"
- Ben Stiller as Khaka Peu Peu in the episode, "The Beak"
- Christine Taylor as Khaka Peu Peu's wife in the episode, "The Beak"
- Laird Hamilton as himself in the episode, "Phineas and Ferb Hawaiian Vacation"
- Phil Lewis as Hotel Manager in the episode, "Phineas and Ferb Hawaiian Vacation"
- Chaka Khan as herself in the the episode, "Summer Belongs To You"
- Clay Aiken as himself in the episode, "Summer Belongs To You"
- Kevin Smith in the episode, "Nerds Of A Feather"
- Seth Mcfarlane in the episode, "Nerds Of A Feather"
- Kenny Ortega as himself in the episode, "Rollercoaster: The Musical"
- Jane Lynch as Jeremy's mom in the episode, "Canderemy," "Run Candace Run" and "Bad Hair Day"
- Jamie Oliver as himself in the episode, "Meatloaf Surprise"
- Davy Jones as Nigel in the episode, "Meatloaf Surprise"
- Peter Noone as Adrian in the episode, "Meatloaf Surprise"