W. D. Gaster is an unseen character in the video game Undertale. He is commonly believed to be a hidden character named "Mystery Man", who appears as a cloaked figure, with his head being visible as a skull cracked in two places. According to lore, he was the royal scientist before Alphys, and responsible for creating the CORE. His life was cut short when he fell into "his creation". His existence is only hinted by characters such as the River Person and Gaster's followers. Similar to Sans and Papyrus, he speaks in a typeface different from other characters, and wholly in capital letters like Papyrus when deciphered into plain text.