The TV star was taken to hospital in Los Angeles in late December after testing positive for coronavirus.
King died at Cedars-Sinai Medical Center, Ora Media, the studio and network he co-founded, tweeted. No cause of death was given in the statement.
King, whose career spanned more than six decades and is estimated to have covered more than 50,000 interviews, had Type-2 diabetes and had suffered from lung cancer, angina and heart attacks in recent years.
During his career, King, hunched over his desk in rolled-up sleeves and braces, quizzed thousands of world leaders, politicians and entertainers.