The cranky old wizard who brings Westley back to life (he was only "mostly dead" after all) and almost steals the show in his brief appearance.
There are some who call him... Tim. He's a fireball conjuring wizard whose warnings to King Arthur and his knights about the Rabbit of Caerbannog go unheeded with bloody results. A truly eccentric performance!
A character so legendary, he's appeared in multiple films (of greater and lesser quality). The best live-action depiction is arguably Nicol Williamson's in Excalibur, and the best animated depiction is from Disney's The Sword in the Stone.
A character who has dominated pop culture for over a decade, no list of movie wizards would be complete without Harry Potter. Of course, you could probably make the entire list solely from characters from the Harry Potter series.
Duh. You can't beat Gandalf! He's an awesome character played by an equally awesome actor!