Bolt, who retained his 100m title in style on Saturday,crossed the line in 19.32sec -- the equal fourth fastest time of all time -- infront of a delirious sell-out 80,000 crowd at the Olympic Stadium.
The 25-year-old's victory meant he bettered the record of UStrack legend Carl Lewis, who won three golds and a silver in the sprints at the1984 and 1988 Games.
Bolt said: "This is the one I wanted and I got it. I'mnow a legend, I'm also the greatest athlete to live.
"I've got nothing left to prove. I've showed the worldI'm the best and, right now, I just want to enjoy myself."
It was also the first time two individual track titles weresuccessfully defended at successive Games since Finland's Lasse Viren won the5,000m and 10,000m in the Munich and Montreal Games in 1972 and 1976.
Bolt led a Jamaican clean sweep of the medals, with trainingpartner Yohan Blake taking silver in 19.44sec and Warren Weir claiming a shockbronze in 19.84sec.
The only thing missing from the race was a new world recordfor Bolt, but he revealed he had felt a flicker of back pain during the race.
"I could feel the strain on my back a little bit so allI did was try to keep my form, run home and when I saw where I was going Istopped running because I knew it wasn't going to be a world record," hesaid.
"The 200m was harder than I expected. I could feel thepressure coming off the bend and that's when I had to focus."
Running in lane seven, Bolt made an explosive start and wasup on Weir in the lane outside him within five paces.
As he rounded the bend, Blake briefly threatened from lanefour, but teeth clenched, eyes on the big screen and at full tilt, Bolt was farenough to slow down a full 10 metres from the line, raising his finger to hislips.
Whether that gesture was aimed at the young pretender Blakeor this season's growing band of doubters, only Bolt knows, but his victoryunderlined his position as the greatest sprinter on the planet.
The London Games are Bolt's fourth global championship since2008.
He has won six titles in the seven individual events inwhich he has competed, his one blip coming when he was disqualified from theDaegu world championship 100m final last year after a false start.
Bolt, also the world record holder in both the 100 and 200m,was not quite his usual playful self in the moments before he settled, an airof seriousness permeating a silenced stadium as he offered a regal-like wave.
Amid the tangible tension, he briefly crossed himself andpointed skywards before settling into his blocks. Once the gun sounded, adetermined Bolt pulled out all the stops to burn off his rivals from the off.
Apart from Bolt, eight men -- Archie Hahn (1904), RalphCraig (1912), Percy Williams (1928), Eddie Tolan (1932), Jesse Owens (1936),Bobby Morrow (1956), Valeriy Borzov (1972) and Carl Lewis (1984) -- have wonthe sprint double at the same Olympics, but only Hahn and Lewis havesuccessfully defended the 100m.
Hahn missed out on his chance of a "double-double"when the 200m was dropped from the 1906 Games and Lewis, after being upgradedto 100m champion in Seoul following Ben Johnson's disqualification, lost to USteammate Joe DeLoach in the 200m.
