Son of American actor Bonar Colleano (1924 - 1958), who died in a tragic road accident in England, and British Rank starlet Susan Shaw (1929 - 1978). An Irish ancestor (boxer) named Sullivan emigrated to Australia, from which came the Colleano (alias) Brothers, who were circus and Vaudevillain performers early in the century. His grandmother (mother of Bonar), a contortionist, became Mark's legal guardian and raised him in Kensington, England, UK. Mostly known for his work as a child and teenager actor.