Who was the first heavyweight boxer to regain the title after losing it?

Floyd Patterson (January 4, 1935 – May 11, 2006) was an American professional boxer who competed from 1952 to 1972, and twice reigned as the world heavyweight champion between 1956 and 1962. At the age of 21, he became the youngest boxer in history to win the title, and was also the first heavyweight to regain the title after losing it. As an amateur, he won a gold medal in the middleweight division at the 1952 Summer Olympics.

In 1956 and 1960, Patterson was voted Fighter of the Year by The Ring magazine and the Boxing Writers Association of America. He was inducted into the International Boxing Hall of Fame in 1991.

After beating Tommy "Hurricane" Jackson in an elimination fight, Patterson faced former Light Heavyweight Champion Archie Moore on November 30, 1956, for the World Heavyweight Championship. He beat Moore by a knockout in five rounds and became the youngest World Heavyweight Champion in history, at the age of 21 years, 10 months, 3 weeks and 5 days. He was the first Olympic gold medalist to win a professional heavyweight title.

Patterson knocked out Johansson in the fifth round on June 20, 1960, to become the first man in history to regain the Undisputed World Heavyweight Championship. Johansson hit the canvas hard, seemingly out before he landed flat on his back. With glazed eyes, blood trickling from his mouth and his left foot quivering, he was counted out. Johansson lay unconscious for five minutes before he was helped onto a stool.