Q
Q is the character from Capcom's 1999 Street Fighter III: 3rd Strike. Expert players are quick to recognize that Q is, undoubtedly, the best character in the game in all places and at all times. Simply selecting him is the equivalent of winning before the match has even started.
However, in an attempt to prevent extreme overuse of the character in tournaments, high-level players continuously rank Q as a low-tier character. Thus, misguided players believe they have incentives to refine their skills with other fighters.
Their efforts are futile.
Background
Q's appearance is that of a tall and clumsy man featuring a trenchcoat, a fedora, and a featureless mask.
While his overall design is based off of several other characters - Robot Detective K, The Question, Rorschach are commonly cited - Q literally has no supplied backstory or motivation. Whether he is human, machine, cyborg, alien, a fallen character of the series, or otherwise will never be determined. Essentially, he is simply an additional character whose plainness lies in stark contrast to the other characters.
Most Street Fighter characters are motivated by extremely broad goals, such as winning tournaments, becoming the world's strongest warrior, meeting new people, and otherwise. Ironically, while these backgrounds work on a basic level, perhaps the never-to-be-understood Q - perhaps an embodiment of random pop culture themes - is the most interesting character of all in the long term.
Or maybe he's just a creepy bastard.
Photobombing
To do - post pictures of Q's ending cutscene, in which he appears in random locations.
Q Elsewhere
In the Summer Forum Battle of 2011, Bum Marceaux and the Four Skin Cancers offered to take requests and provide entertainment in exchange for votes. Much hilarity was afoot, and Q got involved.