If you see a guy with blue hair, and a X on his face. Yeah that's him. He uses the moon to power up and he is not that hard to beat in the game. As long as you grab his Claymore (the name of his weapon) you can use that to defeat him. It will take a couple of times but well worth it for the next fight you get to fight Luxord.
Not much is said about Saix's past, but few fans say he comes from a different dimension. I would like to say that he comes from World of Warcraft (dont make fun of me my friend said that and i stuck with it)
Me: YOUR RIGHT! but that's only canon =3=