A close-up of Cueball from 1063: Kill Hitler
|First appearance||6: Irony|
Cueball is a stick figure character in xkcd, distinguished from other characters by having no distinguishing features (including no hair or hat). The name is unofficial, and pretty much only used on explain xkcd and TV Tropes.
Unlike other xkcd characters, Cueball doesn't necessarily represent the same character from comic to comic, and is not necessarily a unique character in any given strip. Instead, he represents a generic everyman. In several comics, there are multiple such stick figures, any of whom could be called Cueball.
There was at one point a community portal discussion of what to call Cueball and what to do in case with more than one Cueball. Nothing much came of it, but so far it seems that the standard practice is to name the main protagonist (the one with the funniest/defining part) as Cueball and then name the other(s) friend etc. (and make a note that they also are Cueball-like). If it is impossible to discern any of them from the other then neither should be called Cueball.
The character is never actually referred to as Cueball in xkcd. The name was developed by early contributions to explain xkcd. It refers to the visual similarity of Cueball's head to a billiard ball. Randall's transcripts usually refer to the character as "Man 1" etc, although he has at one time referred to him as not terry in his official transcript for 989: Cryogenics. A few comics give a Cueball character a name but only one name, Rob, appears several times (9 in total) for a Cueball. The some debate, mentioned above, was actually mainly about whether all other Cueballs should be retroactively renamed "Rob". Following the logic behind the fact that the "Cutie" character (the female version of Cueball) changed name to Megan, Cueball should have been renamed as Rob. But that suggestion did not get accepted.
 See also