He was banned just before I joined, but I've picked up some stuff over time.
He joined under the premise that he was experimenting with his own personality, every two weeks becoming a different personality as a means of exploring the boundaries of personality. I don't know the exact details, but I'm guessing this is what spilled into multiple accounts. It caused a bit of paranoia at the time about who was and isn't XIII, etc.
Some of the XIII posts give the impression that this experiment was as much one on the community, that he was cognisant of from the start. He said in some posts that he saw a lot of squandered creative talent here, and by challenging the notion of INTP as a category he was trying to challenge what he saw as a comfortable, sleepy pattern that some had fallen into.
It always read like an interesting experiment to me, but it's easy to see why he was banned.