From Wikipedia, the free encyclopedia. John Gavin (born April 8, 1931) is an American film actor and a former United States Ambassador to Mexico. Gavin is half Mexican and fluent in Spanish. He is probably best known for the part of Sam Loomis, Janet Leighs boyfriend in Alfred Hitchcocks Psycho and as Julius Caesar in Stanley Kubricks Spartacus. Description above from the Wikipedia article John Gavin, licensed under CC-BY-SA, full list of contributors on Wikipedia.