Rocco came to Los Angeles from Massachusetts in the early 1960s and trained under Leonard Nimoy of Star Trek fame. He had his film debut in Russ Meyer's Motorpsycho! and would eventually rack up more than 160 acting credits in his name.
He won an Emmy Award in 1990 for his role as a Hollywood agent in Jon Cryer comedy The Famous Teddy Z. Other memorable roles include parts in The Simpsons, Sibs, Magic City, Detroit 9000, The Division, Private Practice and A Bug's Life. He also recurred as Jo's father, Charlie Polniaczek, on NBC comedy The Facts of Life.
Of all the works in his long career, Rocco credits his part in Godfather with making his name. In Rocco’s telling, the role of Moe Greene, a mobster who owns a Vegas casino, was his “biggest ticket anywhere.”
“Every time I ever hear the theme from The Godfather, I always say, ‘Thank you, God,'” he said in a 2012 interview with the A.V. Club.
In March 2004, Rocco guest-starred on ABC daytime soap opera One Life to Live as FBI Chief Christopher Scaletta. In the story, Bo Buchanan (Robert S. Woods) asked Agent Scaletta to reconsider suspending John McBain (Michael Easton). Later, John resigned in a huff when Scaletta had doubts about his work.