Pyramid Head is a Monster in Silent Hill 2.
He's part of several memes. The rape meme occured, because he's shown raping a mannequin ingame. He's also known for having a very good looking ass. This meme was also center of an discussion which occured about the game Dead by Daylight, because his ass was nerfed for no specific reason.
Pyramid Head is assumed to be the alter-ego / manifestation of James Sunderland. Specifically a manifestation of his desire for punishment.