THE MASTER, XEMNAS
The following information is the way Saix interacts with Xemas in the video game version of Kingdom Hearts II. Different games give off different information with this relationship. To view Saix's relationship with Xemas in other games, try each individual section in the main navigation above.
Saix was Xemnas' right hand man through out all of Kingdom Hearts. He was right there with him with the plans he had for the Organization members, and he stayed the most loyal through out the games to Xemnas than any other Organization member. Saix got along so well with Xemnas because they were both very powerful and strong-willed to stay on the path of the ultimate goal. Although Xemnas deceived Saix with the true motives of Kingdom Hearts(spoiler for other games), Saix stood by him the whole time. He eliminated Organization members for the greater good in the eyes of Xemnas. He obeyed every order and went through with almost all of them (except terminating Axel, he managed to do that on his own!).
Saix always asked permission to do things before carrying them out. He asked Xemnas if he was able to "end the charades" before he went forward with plans. He smiles when he hears him say yes and says he's been "waiting to hear that," so he could finish off Sora. However, this makes Saix look like a semi-weak character. He isn't able to think on his own because he is too loyal to Xemnas and his plans. Saix and Xemnas are the closest personality wise, but Xemnas has no intentions of staying by Saix's side the way Saix does about Xemnas. Saix is merely a puppet in Xemnas' eyes and therefore in the end, causing Saix to die. Although he was Organization member 7, he was number two next to Xemnas in strength and importance to the group. Saix stood by his side until the death of him, never being able to have his heart like Xemnas had promised him...