I've heard many theories of Crocodile being born a woman and she was later transformed into a man by using Ivankov's Devil fruit powers (that's why Ivankov could handle him) .What enforces this theory is that he is the only Shichibucai who was seen attending Gol D. Roger's death but who's face was not seen at all. Also in the drawing Oda made of how Crocodile was as a child he is similar to a girl more than a boy. Despite all these I hope he's not a woman as he is propably a future member of the Straw Hats and I wouldn't like it if He joined Luffy despite this. Jk. What's your opinion?