...who have portrayed mentally-challenged characters

• billy bob thornton, in sling blade
• cuba gooding, jr., in radio
• dustin hoffman, in rain man
• giovanni ribisi, in the other sister
• jodie foster, in nell
• juliette lewis, in the other sister
• leonardo dicaprio, in what's eating gilbert grape
• sean penn, in i am sam
• tom hanks, in forrest gump

...who have portrayed mentally-unstable characters

• angelina jolie, in girl, interrupted
• anthony hopkins, in the silence of the lambs
• brad pitt, in fight club
• brittany murphy, in girl, interrupted
• christian bale, in american psycho
• christopher lloyd, in back to the future
• edward norton, in fight club
• ellen page, in hard candy
• glen close, in fatal attraction
• heath ledger, in the dark knight
• helena bonham carter, in fight club
• jack nicholson, in one flew over the cuckoo's nest
• jake gyllenhaal, in donnie darko
• jamie foxx, in the soloist
• jim carrey, in me, myself, and irene
• johnny depp, in sweeney todd: the demon barber of fleet street
• juliette lewis, in kalifornia
• kevin spacey, in k-pax
• natalie portman, in black swan
• patrick fugit, in wristcutters: a love story
• robin williams, in one hour photo
• russell crowe, in a beautiful mind
• ryan gosling, in murder by numb3rs
• sally field, in sybill
• ted levine, in silence of the lambs
• vince vaughn, in psycho
• winona ryder, in girl, interrupted
• woody harrelson, in natural born killers