Cause something has to go here, here's some stuff to know about Garrett that he probably won't tell you (Thief spoilers ahoy):
When Garrett was a young man, he was living on the streets, half-starved. He happened to notice a man moving through the crowd, avoiding people. Seeing this avoidance, Garrett decided that this person must have something valuable so he made a grab for his purse. The man seized him by the wrist and remarked on how strange it was that Garrett could see him. In fact, this was so unusual that he took Garrett back to his monastery.
Garrett spent the next decade or so living with the Keepers. The Keepers are basically Organization XIII: They are secretive, they all know eachother, they have infighting, they all wear black hoods, they love opening portals and they worship keys. The Keepers devote themselves to monitoring activity in the City and maintaining a sort of cosmic equilibrium so other people don't have to. But if the Keepers are Organization XIII, Garrett is their Roxas. Troubled by the secluded, lonely lifestyle he ran away one day and never returned to the Order. But they kept track of him and followed him around, leaving Glyphs and warnings for him and trying to coax him back with limited success. As it so happens, Garrett has some sort of deeper magic, one that even the Keepers are mystified by. Garrett himself is completely unaware of it. But he is the one destined to bear the Key.
Having been trained by Keepers, Garrett possesses unnatural talent. For a thief. He can almost disappear when standing still in shadows. People only a few feet away may not notice him. He can move silently, even in hardened leather boots, and there isn't any lock he can't find a way through. Beyond his stealth mastery, Garrett has the abilities of the Keybearer, and of Keepers in general, much to his own chagrin. He can see things other people can't see, he can read in a wide variety of languages, and he has limited (very limited) psychic ability in that he can hear psions if they mentally communicate closeby.
And that's Garrett. Any questions?
Edit: Also, if anyone is actually interested in seeing where Garrett is coming from, I just noticed that rtoast transcribed my summary of the first two games
over here. It's the only version of my summary online ATM since Ion Storm Forums is gone. Big sad.