100 metres, Men

Usain Bolt won this race in 2008, along with the 200 metres and intially a gold in the 4x100 metre relay, although it was later overturned for a drug disqualification by one of his teammates. At the 2009 World Championships, Bolt won all three titles, and was considered by many as the greatest sprinter in history. But 2011 and early 2012 had not been as strong for him as he struggled with injury problems. At the 2011 World Championships, he false started in the final of the 100 and was disqualified, the title going to his countryman, Yohan Blake. Blake had beaten Bolt one other time in the 100, at the 2012 Jamaican Olympic Trials, and was considered a strong challenger to his title in London. Also challenging the two Jamaicans were Americans Tyson Gay and Justin Gatlin. Gay was the 2007 World Champion at both 100 and 200 metres, but hip injuries had since limited his effectiveness. Gatlin had won the gold medal in this event at the 2004 Olympics, but later had a doping positive and had only returned to competition in 2011.

All four of the favorites made the finals, where they were joined by the third Jamaican, Asafa Powell, former world record hold in the event, but one who seemed to struggle in the biggest international meets; the third American, up-and-comer Ryan Bailey; Dutch runner Churandy Martina, who had formerly competed for the Netherlands Antilles, before the dissolution of that nation in 2010; and Trinidadian Richard Thompson.

The final had an early problem when cretinous spectator Ashley Gill-Webb of Leeds threw a beer bottle onto the track just before the race was to start. Gill-Webb did not know he was seated next to Dutch Olympian judoka Edith Bosch, who quickly subdued him before the authorities arrived to escort him from the stadium. He was later charged with causing harassment, alarm or distress, and pleaded not guilty, although he was found guilty of public disorder in January 2013, and was sentenced to eight weeks of community service in February 2013.

Once the runners were away Gatlin, Blake, Powell, and Gay were out quickly, as Bolt is not known for his starts. But this was better than usual for him and he was in the lead by 40 metres. Powell pulled up from a groin pull although he would finish the race, barely and in last place. In the final 40 metres Bolt pulled away to win in 9.63, the second-fastest time ever, with Blake trailing for silver in 9.75, and Gatlin getting bronze in 9.79. Gay just missed the medals in fourth in 9.80.

Bolt became the third man to defend his Olympic 100 metres title, after Archie Hahn in 1904-06, and Carl Lewis in 1984-88. But both came with an asterisk as Hahn had the always-present 1906 problem, while Lewis only won in 1988 after the disqualification of Ben Johnson for stanozolol use. A few days later, Bolt would also defend his Olympic gold medal in the 200, becoming the first runner ever to defend the 100-200 Olympic double, and he would win three Olympic sprint gold medals, leading Jamaica to a world-record in the 400 relay in London.