I've only skimmed it, but John D'Emilios Lost Prophet: The Life and Times of Bayard Rustin has been very well-received.

In the briefest brief statements about the book, D'Emilio portrays Rustin as the behind-the-scenes guy, the strategist of the Civil Rights movement. Rustin is in that role for many reasons, not the least of which is Rustin's openness about his homosexuality. D'Emilio argues that Rustin's sexuality caused major rifts between Rustin and other major players.

I have it on my shelf, hoping to give it a better read sometime soon.