Sigmund Freud.
Sigmund Freud was a highly noted Human psychologist.
Data began visiting Freud in the holodeck for as psychoanalysis, in 2370, after having nightmares about workers ripping up the USS Enterprise-D and attacking him. He would later have nightmares about the crew and bizarre things that were happening to them.
Freud diagnosed Data as a classic polymorphous perverse. Freud is no help to Data, who later sees Deanna Troi in a counseling session, and she gives him a different analysis and says, "Next time see me before you see Sigmund." (TNG: "Phantasms")