Born in Mississippi, King began performing in the 1940s, going on to influence a generation of musicians, and working with Eric Clapton and U2.
Once ranked as the third greatest guitarist of all time, he had been suffering ill health in recent months.
He was recently taken to hospital with a diabetes-related illness.
A former farmhand, King was awarded his 15th Grammy award in 2009 for his album One Kind Favor.
He was also inducted into both the Blues Foundation Hall of Fame and the Rock and Roll Hall of Fame.
Rolling Stone magazine placed him behind only Jimi Hendrix and Duane Allman in its list of the 100 greatest guitarists of all time.
Until recently, King performed in at least 100 concerts a year.