The beholder is a monster shaped as a floating giant spherical eye ringed with eyestalks, firing different magical rays from its central eye and from each stalk. The idea of a floating one-eyed orb is a generic motif owned by no one, but the name "beholder" together with this specific design — eyestalks combined with an antimagic ray — is Product Identity held by Wizards of the Coast and excluded from the OGL/SRD.
This hub therefore treats the concept of "a floating giant eye" as a shared asset while making clear that the name beholder and its particular combination of form and powers are protected trademark. The image of a being that sees everything at once through countless eyes is not far from the gaze motif of cosmic horror, like Yog-Sothoth pervading all of space and time.