Q has always been my all time favourite Street Fighter character. He's like a mysterious mix of Darth Vader, Rorschach, and Inspector Gadget. There isn't much backstory to Q.. He apparently appears all around the world when disasters happen. Nobody knows if he's good/bad or what his purpose is or why he's a robot. It's like he's some kind of 'Time Cop' or something.

Q's first appearance was in Street Fighter II as a spectator cheering in Ken's stage.

OH! And here's a little combo video to get an idea of what Q can do ;)
Q COMBO VIDEO!! CLICK ME NAOW!