William Dafoe is a great actor, but I don't think he would QUITE fit Magus. William Dafoe's characters seem to have a little bit of a crazy/wacko edge to them. Think Green Goblin, or the detective from Boondock Saints.
Kiera Knightley I would disagree with as well. Marle has to have a little bit of an immaturity to her. Maybe Hilary Duff? I wouldn't necessarily WANT her, I'm jsut talking that kind of immaturity level.
Typecasting Willem to roles is a dumb idea, that was two of his more recent films. Like you said he is a great actor, and he obviously can play the role. Willem has experience playing villans, what villans has Adrian played (I am asking because I only know him from the Pianist)?
Marle isn't immature, she just doesn't think things through. She does stuff based on her emotions, instead of rationalizing out the events and choosing the best action. And Hillary Duff can't act, so never mention the name again.
Having played a sort of role before is not neccessarially important. If someone can act decently well, there is a good chance they can do it. The thing is, Willem Dafoe is plainly far too old for Magus. Yes, he could be a Magus in his 40s... but not the one from the game. It would be impossible.
Well, here is a third idea. Michael Wincott. He has a better voice for the role than either of the two, and plays a devilish-seeming bad-guy even better than Dafoe, I think. He was Guy of Gisborn in Robin Hood Prince of Thieves. He was Count Rochefort in the Three Musketeers. And he was the jailkeeper in the more recent Count of Monte Cristo. His voice, I think, is one of the best in movies for Magus - he also did the voice of the Prophet in Halo 2 that says: 'There are those who thought this day would never come. What are they to say now?' The only problem is, he's a little older now.
Here, for example, is a picture of him, and a sound byte.
http://www.michaelwincott.org/Wavs/dorleactime.wavhttp://www.michaelwincott.org/Wavs/Rochbold.wavSo, for consideration, here are the three candidates to play Magus:
Willem Dafoe - an experienced actor, 50 years old. (I tried to find a picture where he looks grimmest and with the longest hair.)
Adrien Brody - A fair actor (or at least what I saw in the Village), 32 years old.
Micheal Wincott - Another experienced actor, with a voice arguably the best of the three - 47 years old. This picture is... 13 years old, so he has aged a little since then.
Personally, my vote still goes with Adrien Brody for his younger years, but if an older actor would be alright, then it would be Michael Wincott.
Should I start a seperate poll on this question, who would be better for Magus?