Visions & illusions
(covers information from a vision or illusion)
You may be looking for Mavek, a Cardassian.

Mavek was a Tilonian working at the Tilonus Institute for Mental Disorders. He was a character in a delusion created by the neurosomatic technique used by Suna in his attempt to extract strategic information from Commander William T. Riker. He was an orderly who constantly tormented Riker both physically and mentally. (TNG: "Frame of Mind")

Mavek was played by Gary Werntz.