Which athlete became the first person to successfully defend an Olympic decathlon title?

Robert Bruce Mathias (November 17, 1930 – September 2, 2006) was an American decathlete, two-time Olympic gold medalist in the event, a United States Marine Corps officer, actor and United States Congressman representing the state of California.

In the 1948 Summer Olympics, Mathias's naïveté about the decathlon was exposed. He was unaware of the rules in the shot put and nearly fouled out of the event. He almost failed in the high jump but was able to recover. Mathias overcame his difficulties and with superior pole vault and javelin scores was able to push past Ignace Heinrich to win the Olympic gold medal. At age 17, he became the youngest gold medalist in a track and field event.

At the Helsinki Summer Olympics in 1952, Mathias established himself as one of the world's greatest all-around athletes. He won the decathlon by the astounding margin of 912 points, which established a new world record, and he became the first person to successfully defend an Olympic decathlon title.