Question: who played mark on the show the rifleman?
Answer: John Ernest Crawford

John Ernest Crawford ( born March 26 , 1946 ) is an American character actor , singer , and musician . At age 12 , Crawford rose to fame for playing Mark McCain , the son of Lucas McCain ( played by Chuck Connors ) , in the popular ABC Western series , The Rifleman , which originally aired from 1958 to 1963 . Crawford first performed before a national audience as a Mouseketeer .