Earl Hammond began acting in radio at the age of 7 and continued working in that venue throughout his life In the 1940s he had a regular role as a young lawyer on a radio soap opera From 1974 to 1982 he acted on the CBS Radio Mystery Theater appearing in 189 episodes more than 12 of the entire run of the 1399 episodes of that radio series Hammond started his television career in the early 1950s his first major role being as a regular called Sergeant Lane on the DuMont police drama Inside Detective aka Rocky King Detective starring Roscoe Karns At the same time he also was the first of three actors to portray the title character in the shortlived ABC TV sciencefiction adventure series Buck Rogers which ran from April 15 1950 to January 30 1951 In the mid1950s he had a major role in the dailynoontime CBS television soap opera Valiant Lady as Hal Soames the married love interest of the widowed title character Hammond was perhaps best remembered for providing the voices of MummRa Jaga and other characters on the 1980s animated TV series ThunderCats and for being the voice of villain MonStar on the 1980s animated TV series Silverhawks He also was the voice of the Transformers villain Megatron in a series of childrens readalong books In 1994 Hammond was selected from among several hundred actors who auditioned to be the voice of Pope John Paul II on the audiotape version of the Random House book Crossing the Threshold of Hope The publisher said the pope personally selected Hammond