Alexander the Great
The conqueror who once had an empire stretching from Greece to Egypt to northern India and is considered one of the greatest military commanders of all time was also very likely gay, or at least bi. His military conquests led him to the farthest reaches of the known world at the time, and he is responsible for much of the cultural exchange that happened in this era. In his personal life, Alexander was not particularly interested in women, although he took a number of wives and kept a harem in the tradition of kings before him, there were done mostly for political reasons. He had a general that he kept close companionship with, and he did not father any sons until late in life.