The Jamaican track star won the 100-meter final in an Olympic-record 9.63 seconds Sunday evening.
Bolt broke his previous record time of 9.69, set at the 2008 Olympics in Beijing. Bolt was .05 seconds from landing a new world record (9.58), which he set at the 2009 world championships.
Fellow Jamaican Yohan Blake won silver (9.75), and Justin Gatlin of the United States won bronze (9.79).
Bolt had faced doubts about whether he'd dominate again coming into the London Olympics. He had back and leg issues, and even his personal life came under some scrutiny, with some accusing him of partying a little too hard.
On Sunday there were no more questions. Bolt became the first man to defend the 100-meter race since Carl Lewis in 1988.