From imdb.com:
'Marine fighter pilot during World War II, McMahon sold vegetable slicers on Atlantic City's boardwalk to put himself through Catholic University in Washington, DC. His next assignment was as a fighter pilot during the Korean War. After that he resumed his career in television. In 1959 he was hired as Johnny Carson's straight man on the daytime quiz show "Do You Trust Your Wife" (1956). When Carson succeeded Jack Paar on NBC's "The Tonight Show Starring Johnny Carson" (1962), he took McMahon with him. This job would last for 30 years and make McMahon wealthy and famous. He would also appear in made-for-TV movies and host daytime game shows in the 1960s and 1970s. In the 1980s McMahon would team with Dick Clark on "TV's Bloopers & Practical Jokes" (1984) and host his own long-running talent show, "Star Search" (1983). He would also make commercial appearances for a multitude of products.'