His family said in a post on Instagram on Friday night: “Our hearts are broken.
He dropped out of school and turned to street robberies before eventually finding his outlet in the ring.
Foreman won the heavyweight gold medal at the 1968 Olympics in Mexico City, aged 19, before turning pro and winning 37 consecutive matches. He lost only five bouts over his career.
He recalled that his preaching started small, on street corners and with friends, then grew.