Glen Burke is often credited with being the first openly gay major league baseball player. It probably depends on your definition of “openly,” as he did not make his sexual orientation known to the public until after he retired, though he was out to many of his teammates with the Dodgers and the A’s. I guess how you characterize it all depends on how much stock you put on someone being out “in the locker room,” literally speaking.
At any rate, Burke wrote a book about his life before he died in 1995 and a documentary as made about him and aired in 2011. Now, a Hollywood star is trying to get a feature film made:
Also: Burke is often credited with inventing the high five, so whoever they cast has to be able to do that.
(thanks to historiophiliac for the heads up)