Tuco was played by the great Eli Wallach. Tons of roles over the years including several other westerns (Magnificent Seven, How the West was Won, The Misfits....) and has a nice part in the the Holiday with Kate Winslet. He also did commercial voiceovers for Toyota trucks for years.
Damn. He had a bunch of solid roles in a bunch of good movies. In addition to some of the other roles listed, he played Bump Bailey in the Natural, the player who died after crashing through the OF wall.