NEW YORK, March 22 — American George Foreman, one of the great second acts in sports who reclaimed the heavyweight boxing title after coming out of retirement and became a celebrated product pitchman, died yesterday at age 76, his family said.

“A humanitarian, an Olympian, and two time heavyweight champion of the world, He was deeply respected — a force for good, a man of discipline, conviction, and a protector of his legacy, fighting tirelessly to preserve his good name — for his family,” the family said, describing Foreman in a post on Instagram.

An intimidating, thunderous puncher who lost his first title to Muhammad Ali in their famous “Rumble in the Jungle” in 1974, “Big George” was a more rotund, jovial figure when he knocked out Michael Moorer for his second crown two decades later.

Foreman’s comeback and the fortune he made selling fat-wicking electric cooking grills made him an icon of self-improvement and success for the Baby Boom generation.

Soon after his birth in Marshall, Texas, on January 10, 1949, his family moved to Houston where he and his six siblings were raised by a single mother. Growing up poor in the segregated American South, Foreman dropped out of junior high school and used his size and fists in street robberies.