Pedobear
Pedobear is a variation on Kuma, a meme character that first appeared on 2channel. It was adopted on the 4chan boards and given a different name and personality. Typically Pedobear represents a pedophile and is often used by visitors of 4chan to signify masturbatory enjoyment of lolicon, as in the phrase "Pedobear approves".
The original character appeared on 2channel in the form of Shift_JIS art, and is known as Kuma. He is known on 2chan for his freedom of will and is often found in images that depict sleeping with children, thus his name became Pedobear on 4chan. An example picture is Kuma attacking Ronald McDonald, the latter in this case representing corporations. The choice to use this particular 2channel character was made by an anonymous 4chan member, probably at random or for comedy value.
Pedobear quickly grew in popularity on 4chan, and was edited into various humorous pictures. There have been many different incarnations of Pedobear, including 3D renders, strange sketches and even a secret top hat wearing variety; but the original bear is still the most recognizable.
Pedobear is a popular character on YTMND, and sees usage on many internet message boards. He is often seen with the phrase "Do you sometimes pee in the bath?"