Mind flayer using psionic attack, by Tom Wham from the AD&D Monster Manual, TSR, 1977.
d&d 3.5e-5e art: Epic Fantasy Arte
d&d 3e art: same but weirder
ad&d 2e art: stuff that looks like things a drug dealer obsessed with led zeppelin would paint on his van
everything earlier, including this: editorial cartoons from the Neverwinter Herald