Film

Mamakos was in eight movies in his first seven months in Hollywood.^[2] Mamakos appeared in Trail of the Yukon (1949), in which he and other supporting players offered what a Variety review called "stock performances".^[3]

Television

He had a recurring role as Jean Lafitte on the ABC western The Adventures of Jim Bowie. He also appeared as a Lionian Henchman in Tarzan and the Slave Girl (1950) starring Lex Barker. Mamakos made three guest appearances on Perry Mason from 1962 to 1966, including the role of murderer Nick Paolo in the 1962 episode, "The Case of the Stand-in Sister", Juan Carlos Ramirez in the 1964 episode, "The Case of a Place Called Midnight" and murder victim Olaf Deering in the 1966 episode, "The Case of the Sausalito Sunrise". He also appeared in 1966 in episodes 41 and 42 of Batman. He appeared in several episodes of the TV show The Lone Ranger.

Mamakos is also remembered as Happy J. King, the Metropolis crime boss who engaged a European criminal scientist to invent "synthetic kryptonite". Kidnapping Lois Lane and Jimmy Olsen, King came closer than any other criminal in ridding the Earth of Superman (George Reeves). This event was recounted in "The Defeat of Superman", the sixth episode of the second season of The Adventures of Superman which first aired on October 24, 1953. He co-starred on Daniel Boone in 1970 as a Cherokee chief in episode 18 "A Run for the Money".