connor93. you can't trust Wiki, any one who wants to can edit it, so it's best you ask th creators about it.

Zack, that i have been told, is actually Clouds brother that died. when that happened cloud when insane and took over Zack's life. If you play the original FF7, the entire game is Cloud with both the memories of Himself and Zack. And since he has both he goes nuts because he doesn't know who he is. and needs to sort out his life.