LONDON — Former heavyweight boxer Henry Cooper, one of Britain’s most popular sportsmen who was best known for knocking down Muhammad Ali while he was still known as Cassius Clay, died Sunday. He was 76.

The first boxer to be knighted and receive the title “Sir” from a British monarch, Cooper died just two days before his 77th birthday. Cooper floored Ali, then an up-and-coming contender named Clay, in a 1963 nontitle fight at Wembley Stadium.

Cooper threw a trademark left hook — known by fans and British boxing writers as “‘Enry’s ‘Ammer,” toward the end of the fourth round, catching Ali flush on the jaw and sending him through the ropes to the canvas.

Ali won the bout by technical knockout in the next round while trailing on the scorecard.