Daniel Day-Lewis. He's actually managed to fool me a few times and I (briefly) didn't realize that it was him on the screen.
It's a neat trick to pull off, considering how many actors rely on their looks and fame to draw the crowds. Truly disappearing into a role is harder than it sounds, precisely because of that. I appreciate that Brad Pitt hasn't strictly relied on his pretty-boy looks and has frequently taken low-key supporting roles, using plain-old acting craft, as well as distracting character tics, heavy facial hair and other make-up tricks to obscure his recognizability.
Identical cousins! (But not two of a kind!)
And don't forget cousin Betsy from Chatanooga, Tennessee!
You did a great job, Flip! (Or is that your cousin from Louisiana Beauregard Flipper?
If you watch Barefoot in the Park, it's hard to realize it's the same two actors as those in Electric Horseman. I think there's another Redford/Fonda movie out there, but I can't remember what it is at the moment.
Is it They Shoot Horses, Don't they? Whoops Redford isn't in They Shoot...! It was The Chase.
Sounds right. Anyway, they surely lost themselves in the characters. And I don't think it has to do with their "age" at all.