Oscar Bonavena, born September 25, 1942 in Buenos Aires, Argentina – died May 22, 1976 near Reno, Nevada, United States, was a professional boxer.

Oscar Bonavena travelled back and forth between America and his native Argentina, fighting in both countries and enjoying reasonable success. As a heavyweight contender, he first got attention after winning over the Canadian champion, George Chuvalo then going the distance against hard-hitting great, Joe Frazier on two occasions, the second for the WBA heavyweight championship in December of 1968. Two years later he fought Muhammad Ali, losing in the 15th and final round on a knockout. It marked the only time that Bonavena was stopped in a professional career where he earned a record of 56 wins, 9 losses and 1 draw.

In February of 1976 Bonavena fought what would be his last fight against Billy Joiner in Reno, Nevada. Liking the nightlife, he stayed in the Reno/Las Vegas area where he was murdered a few months later by Ross Brymer, a bodyguard at the famous brothel, the Mustang Ranch. Brymer served 15 months in prison for killing Bonavena after pleading guilty to voluntary manslaughter.

Oscar Bonavena was buried in the Cementerio de la Chacarita in Buenos Aires, Argentina.