Leonardo da Vinci
You probably need no introduction to the world's greatest thinker, inventor, scientist, and artist, Leonardo da Vinci. We are all likely familiar with his Mona Lisa or The Last Supper; we are all likely aware that he conceptualized flying machines hundreds of years before they were realized. Perhaps less well-known is his 1476 accusation of sodomy. The charges were later dropped (thankfully, as sodomy was punishable by death at the time), but it is the most direct reference to any sexual relationship of da Vinci's which survives. Historians contend that his preoccupation with the male form (see the Vitruvian Man), as well as his close relationships with several pupils and his propensity for erotically-charged artwork featuring male figures (including his famous St. John the Baptist), are evidence that Leonardo was gay, or at least bisexual. While there is no definitive proof, the lack of female companionship, particularly for such a respected, talented, and likely wealthy man, points toward the likelihood of his homosexuality (not to mention a direct reference in da Vinci's notes to "the act of procreation" being "disgusting").