Xigbar!

"The Chamber of Repose  . If you recall, that's where we spent our time researching the darkness that resides within people's hearts. It's a graveyard that was sealed by order of Ansem the Wise. The first thing Xemnas did once he got rid of him was to undo the seal and build a room in the back. Ever since then, he holes himself up in that room when he can, and he talks to someone . But who? For all I know, he's the only one in that room."