L0L Megan is a stick figure character in XKCD. She is the second-most frequently appearing character after Cueball, and the most frequently appearing female character. She is distinguished by her black shoulder-length hair which generally appears to be parted in the middle in front, and is draped behind what are presumably her (undrawn) ears. Megan frequently appears with Cueball as a couple. Megan is also the name of artist Randall Munroe's wife.
Unlike most other characters, Megan does not necessarily represent the same character from comic to comic, but unlike Cueball, the character has been referred to by name in comics from time to time. She is essentially the female equivalent of Cueball, apparently representing the everywoman to his everyman. Megan does, however, appear to have slightly more specific personality traits in some comics than Cueball. At times, she has very odd habits and is sometimes shown to be very focused and intent on a goal, more like Black Hat.
Early xkcd comics often feature a Megan-style character who may or may not be Megan. Randall appears not to have standardized his character lineup early in the comic's run, and as a result, early characters sometimes have similar hair to Megan, but some different features, and are difficult to identify as Megan or not.