Happy 52nd Robert!
Terminator 2: Judgment Day (1991)
This is the first role I remember seeing him in and I still think it is his best role.
In this sequel to 1984 sci-fi hit, Robert plays the more advanced terminator, the T-1000.
It was directed by (like the original) James Cameron and also stars Arnold Schwarzenegger (of course), Linda Hamilton, and Edward Furlong.
The Faculty (1998)
This high school sci-fi film was directed by Robert Rodriguez (Desperado, From Dusk till Dawn, Spy Kids, Sin City....)
In addition to Robert, who stars as the school's coach, it also stars Josh Harnett, Elijah Wood, Salma Hayek, Jon Stewart and Christopher McDonald.
Walk the Line (2005)
Robert plays Ray Cash, the father of Johnny Cash in this amazing biopic about the early days of Johnny.