Illwinter's next project

[S.R. Krol]

The thing is though I have never seen Beholder written as Beholder(tm) in any D&D book. While the wiki claims it is part of the "identity" of D&D and therefore is not in the SRD I did a quick search for "Yaun-Ti" which they also consider the same. Lo and behold there is an entire module dedicated to the Yaun-Ti from a third party, Goodman Games. I'm also guessing you can find beholders in third party adventures.

And as pointed out beholders, while often not called beholders, have appeared in computer games since the 8-bit days.