Much can be said about Xenogears and Xenosaga, and not all of it very flattering. Nevertheless, one thing most people seem to like is the ensemble cast of bad guys. They come in all shapes and flavors, some sympathetic and some not. Some badass fighters while others are clever manipulators.
The question is - who is your favorite of any Xeno game?
Grahf?
Id?
Krelian?
Margulis?
Albedo?
Yuriev?
For me it's a tough call between Grahf and Dmitri.
The thing is, these two are actually quite similar. The theme of Xenogears was Grief and the theme of Xenosaga was Fear. You could argue each villain (and the heroes) relate to these themes of course but I feel Grahf and Yuriev best represent them. Grahf, as a part of The Contact, has experienced more grief than just about anyone. Over 9,000 years of having the love of his life die horribly in front of him while he could do nothing about it.... He's witnessed numerous wars, genocide, the hope being sucked from the entire population of the world... After enduring all this across the aeons he simply says smurf it and decides to help end the cycle of grief. Euthanize the Universe.
Yuriev meanwhile embodies Fear because of his contact with U-DO. Fear is literally the thing that guides every step he takes across the entire series. It was fear and fear alone that nearly allowed him to win and become the most powerful being in existence. The problem was...well, the game put it better than I can. "In order to conquer his fear, he chooses to absorb that fear and become that fear himself." In spite of all his great triumphs and manipulations, you could really argue that Yuriev just kept falling and getting more and more pitiable. Anotehr quote that comes to mind to describe him is Fatman's quote from MGS2: "I am the greatest humanity has to offer - and the lowest."
In order to "defeat" these timeless banes of humanity, Grahf and Dmitri both embarked on extreme and destructive paths to "salvation." That's a huge reason I love them so much.
But that's me. How about you all?