Robert Mueller III, the long-serving FBI director who later served as the special counsel overseeing the investigation into Russian interference in the 2016 election, has died. He was 81.

In a statement, a spokesperson for the law firm where Mueller worked, WilmerHale, told NBC News, "WilmerHale mourns the passing of our friend and former partner, Bob Mueller. Bob was an extraordinary leader and public servant and a person of the greatest integrity."