World light-heavyweight champion

In 1968, Foster got his first shot at a world title. At Madison Square Garden in New York, on the night of March 24, Foster became world champion by knocking out Dick Tiger in four rounds. Tiger had been a two-time world middleweight champion and was defending his world light heavyweight crown that night. Foster then decided to box at heavyweight once again, and beat Charlie Polite by a knockout in three. He ended that year defeating Vick again, and his future world title challenger Roger Rouse, both by a knockout.

In 1969, he began by rising off the canvas to knock out Frank DePaula in the same first round and retain his belt. It is believed that was the first time ever a boxer won a world title fight in the first round after being floored in that same round.^{[citation needed]} It is also believed that that fight is one of only three times that's happened...^{[citation needed]} the second time being in 1984, when Juan Meza rose off a knockdown to dethrone world Jr. Featherweight champion Jaime Garza in the same first round too. It also happened in the 21st century, when Kendall Holt was dropped twice, only to knockout Ricardo Torres in round 1, for the WBO 140 lb title.

Foster's next fight in 1969 was against Andy Kendall, whom he beat in four rounds by knockout, to once again retain the crown. He closed the 1960s with two more knockout wins.

Frazier vs Foster

In 1970, Foster made two more trips to the heavyweights. In the first, he beat fringe contender Lee Wallace in six rounds by knockout. This was followed by a return to the light-heavyweight division to defend his title against Rouse. Infuriated by some comments that Rouse's manager had made before the bout concerning the fact that even though Foster knocked out Rouse in their first bout he was not able to drop him, Foster dropped Rouse five times en route to a fourth-round knockout victory. A knockout in 10 to retain the title against Mark Tessman followed, and then he was given the chance to challenge for the world heavyweight title. Facing world champion Joe Frazier on the night of November 18 in Detroit, he was knocked out in two rounds.

After defeating Hal Carroll by a knockout in four rounds to defend his crown, the WBA stripped him of the title, but he was still recognized by the WBC as a champion. Foster became enraged at the WBA, which proceeded to have Vicente Rondon of Venezuela and Jimmy Dupree fight for the world title. Rondon won, becoming the second Latin American world light-heavyweight champion (after José Torres), and Foster set his eyes on him. Foster went on defending his WBC title, and he defeated challengers Ray Anderson, Tommy Hicks, and Brian Kelly. Of those three, it was Anderson who was the only one to last the 15 round distance with Foster.

Ali vs Foster

Foster and Rondon met in Miami on April 7, 1972, in a unification bout. Foster became the undisputed world champion once again, by knocking Rondon out in the second round. In his next fight, he used what many critics have called one of the best punches in history to retain his title by a knockout in four against Mike Quarry. Foster then went up in weight and faced former and future world heavyweight champion Muhammad Ali, on November 21, 1972, in what was legendary referee Mills Lane's first bout of note as a referee. Foster lost to Ali by a knockout in the eighth, after being knocked down 7 times.

In 1973, Foster retained his title twice against Pierre Fourie, both by decision. Their second fight had a distinct social impact because it was fought in Apartheid-ruled South Africa, Foster being Black and Fourie being White. Foster became a hero to South African Blacks by beating Fourie the first time around, and in their rematch, the first boxing fight in South Africa during Apartheid featuring a White versus a Black, he cemented that position by defeating Fourie on points again.

Piet Koornhoff was the South African Minister of Sport at that time and he had to be persuaded to allow the fight. He had to amend the regulations relating to the prohibition of "mixed sport" in order to do so. Bob Foster was allowed into the country on condition that he refrain from making any political comments or speeches. In a post fight interview he diplomatically responded to a specific question that he liked the country and would be willing to come back again. This explains the sentiment of Mark Mathabane as noted in his autobiography Kaffir Boy, that South Africa's black population felt betrayed by Foster since he didn't address Apartheid during his time in South Africa.

His last defense as world light-heavyweight champion came in 1974, when he was dropped by Argentinian Jorge Ahumada, but managed to keep the title with a draw. After that, he announced his retirement, leaving the world's light-heavyweight championship vacant.^[5]

Foster returned to boxing in 1975, before retiring from the sport in 1978 at the age of 36.