Phineas Flynn was a kick butt superhero known as Mr. Improbable, until his heroics caused legal issues and it was decided that superheroes were banned. After that time he married fellow superhero Isabella, AKA Flexi-Girl, and had three kids, Adrian, Julia, and Thomas, who also inherit superpowers (minus Thomas). Phineas is called back into action when his archenemy resurfaces, but he'll need the help of his family.
Phineas Flynn/Mr. Improbable- Once a famous superhero, Phineas finds it difficult to lead a normal life, and longs to relive the glory days, but deeply cares for his family. His power is super strength.
Isabella Flynn/Flexi-Girl- Once a lovely superheroine, now a busy housewife, she tries her best to make her husband feel comfortable with family life, but not afraid to take a risk. Her power is full body elasticy.
Adrian Flynn- A high strung pre-teen boy, he's insecure with his powers, and wants to be a normal kid, he often needs the support of his family. His powers are invisibility and the ability to generate force fields.
Julia Flynn- A hyperactive little girl, who wants nothing more than to show-off her powers, but is held back by her mom. Her power is super speed.
Thomas Flynn- The Flynn family infant, he has no powers.
Ferb Flecther/Freezer- Phineas' step brother, and fellow superhero, he hates his normal life as much as Phineas does, but unlike him, believes it's for the better. His power is generating icy cold winds.
Arnold "Big" Biz- A mad entrepenuer and Phineas' archenemy, believes that the world is "like a business, the more of it you have, the more succesful you are". He disappeared in a battle with Mr. Improbable fifteen years ago, believed to have been dead.
Buck Barns- Mr. Biz' nervous teenage assistant, he constantly annoys Mr. Biz saying he is "bad for business".