Ooo, that’s a good question with a rather complicated answer. Pyramid Head or the Red Pyramid Thing, is one of the most iconic characters from the Silent Hill series. However, who he is can be rather subjective.
Pyramid Head first appeared in 2001’s Silent Hill 2. In that game, James Sunderland arrives in the eponymous town of Silent Hill after receiving a letter from his dead wife. While he’s exploring an apartment block, he discovers Pyramid Head assaulting and then killing a mannequin leg monster. He’d then continue bumping into the monster who would menace the protagonist throughout the search for his wife. The monster was something of a secondary antagonist if you consider either Mary/Maria or the Town as the primary one.
Pyramid head appears as a disfigured man in a butcher’s apron with a massive, rusted metal mask obscuring his head. True to his name, the mask is in a pyramid-like shape. He tends to wield extremely large weapons, including a massive knife and a large spear.
Pyramid Head’s existence is described by James as a manifestation of his guilt and a need to “punish [him] for [his] sins” (Spoiler: he killed his wife). He supposedly exists only in James Sunderland’s head, and is manifested by the town of Silent Hill.
Until he isn’t. Pyramid head was such a memorable character that he sort of became the face of the Silent Hill series. As such, he appeared in the 2006 Silent Hill films, as well as 2008’s Silent Hill: Homecoming, with minor cameos in Silent Hill: Origins and Silent Hill: Downpour. Explanations have been contrived for their presence, but art director and Pyramid Head’s creator insists that he only exists as part of James’ psyche and doesn’t belong anywhere else.
That might be taking the subject too seriously. Despite how Pyramid Head might have been intended, he’s become the de facto spokesmonster for Silent Hill. For better or worse.