Another case of greatness being thrust upon him, but Kevin Kline’s character in Dave was a mild-mannered temp agency owner who ended up pretending to be the US President.
It’s a bit of a stretch, but maybe Will Smith’s character in the first Men in Black might qualify - an ordinary cop who is suddenly let in on “the big secret” and needs to save the Earth from aliens.
I don’t know that Harry Potter was ever wimpy, more like kept down. I mean, in wizarding terms, he was unusually powerful from the start.
Neville Longbottom comes to mind, though.
Arthur P. Dent
Chuck Lumley (Henry Winkler) in Night Shift.
I think that Arthur just continued being a nebbish in space. I don’t recall him becoming particularly heroic.
I think Rango fills the bill, going from fantasizing terrarium pet to western hero.
Tucker, from Tucker and Dale Vs. Evil.
Maybe not heroic, but it seems to me that in So Long … he became a lot less nebbishy and a lot more like a citizen of the galaxy.
Jamie Lee Curtis character in “True Lies”. Dreams of adventure and excitement and discovers a surprising talent for it when it’s thrust upon her.
Fielding Mellish in Bananas.
Yes, even in the beginning, he would snark back, especially at Dudley. Being fast on his feet (plus a little wild magic) helped him get away with it.
Certainly. Besides his Level in Badass and being a Rebel Leader, he also gets to deliver an As Long As There Is One Man speech. Having sufficiently inspired the Resistance for the moment, and also been set on fire, he proceeds to destroy the last soul jar, clearing the way for Harry to finish the job. There’s a reason Neville has become the Memetic Badass of the setting.
No, no, the wild magic that destroys peace was an entirely different set of stories (about a sort of anti-hero who came through at the end).
The Hulk?
Jerry Lewis’ Nutty Professor?
Gary Cooper in “Along Came Jones”
Speaking of Cooper, almost everything he did.
Hooks in Police Academy “Don’t move dirtbag”
John Ritter’s character in Real Men
Frodo. And Sam.
Didn’t the original Billy Batson sort of stumble on being Captain Marvel (by learning the magic SHAZAM!)?
Wart in T.H. White’s The Sword in the Stone
Dorothy in the Baum books of Oz?
Babe (Dustin Hoffman’s character) in Marathon Man.
The Duchy of Grand Fenwick