What tv show had the most characters go through personality changes

[Sacred Knight]

In regards of Big Bang Theory if we're talking changes that don't really reflect growth but just a sudden change in direction, really only Bernadette and Amy fit. Bernadette was not introduced with her tiny firecracker personality. Nor was Amy introduced with the strong sex drive she'd later acquire out of thin air. So those two genuinely went through a change by writing mandate. And Stuart in regards to supporting characters. The others had pretty much organic growth, not counting the early season 1 episodes where an original sitcom cast typically are still being fine-tuned.

[Somecrazyaussie]

Most of the characters from ER (Peter Benton and John Carter especially).

Phil Mitchell was the level-headed calm one out of him and his brother, Grant on EastEnders (Grant was a loose cannon). Then, after his alcoholism storyline, as well as the departure of Grant, Phil became a amalgamation of the two.

Paul Robinson on Neighbours. Was always a villainous character, but when they brought him back after 10 years of being away, they ramped it up to cartoonish levels. Even the writers recognized this and explained it as being a result of a brain tumour.

[Midvillian1322]

Maybe "Buffy the Vampire Slayer" considering how long it lasted and the time period of the characters' lives. The whole point of the show was how you change from adolescent to adult.

Yea that and Angel come to mind. Characters were drastically different by the end.

[Ikari]

Yea that and Angel come to mind. Characters were drastically different by the end.

Yes Buffyverse had some crazy changes. Willow was a shy computer nerd girl and fans were certain 'oh she will become a Watcher, right?' and when they asked Whedon about that, he said 'Mmm no, something else is planned for her...' and boy it was.
Looking back to the first season, it is pretty insane to think that not only Angel-Cordelia would become a thing, it would seem completely natural character-wise and fans actually would demand it. Anyone who would have suggested that back then would have been committed right away.

[LoganAlpha30X33]

I think that some of the Angel and Cordy stuff was greatly helped by them not being on Buffy's show anymore...

[TriggerWarning]

Yes Buffyverse had some crazy changes. Willow was a shy computer nerd girl and fans were certain 'oh she will become a Watcher, right?' and when they asked Whedon about that, he said 'Mmm no, something else is planned for her...' and boy it was.
Looking back to the first season, it is pretty insane to think that not only Angel-Cordelia would become a thing, it would seem completely natural character-wise and fans actually would demand it. Anyone who would have suggested that back then would have been committed right away.

Also after Wesley's first appearance on Buffy, no one would believe what he became.

[green_garnish]

To me, the Grand Champ was M*A*S*H. Hawkeye, Radar, Klinger, BJ, Winchester, and (especially) Hot Lips all walked some long, developmental roads.

Margaret had a genuine change. Hawkeye sort of did. Klinger stopped wearing dresses but had no real personality change. Winchester certainly did not. Radar kind of. BJ not even close.

[ChrisIII]

Not sure if it counts but both CSI and NCIS pretty much had the team leaders-Grissom and Gibbs-be far more upbeat in their first season before making them far more reserved and aloof.

Also kind of happened to Laurence Fishburne's character, he was a more of a scientist who was used to desks who was trying to learn how to do be a trainee CSI before the next few seasons revealed he was basically Dexter.