Beholders are one of Dungeons & Dragons' most iconic original creations. They have no prior basis in mythology, pulp, or fantasy, unlike so many of the game's most beloved monsters. Instead, they're a piece of fantasy history that begins with early D&D books. Beholders' defining eye-centric design and otherworldly powers have made them go-to villains for Dungeons & Dragons for decades.
Source：https://www.cbr.com/dnd-beholder-guide-how-to-run/
