Carl Gustav Jung (1875-1961) was a famous 20th century Earth psychologist and psychiatrist from Switzerland who founded analytic psychology.
Deanna Troi quoted Jung while helping William Riker who was having disturbing thoughts while performing the play Frame of Mind in 2369. (TNG: "Frame of Mind")
He devised the concept of seeking therapeutic results from within the imagination, called active imagination technique. Native Americans had begun a similar practice centuries earlier as they consulted an animal guide as counselor during a vision quest. (VOY: "The Cloud")
Therapists who followed Jung's teachings would explore synchronicities in recent events in order to to retrieve an unconscious memory. In 2374, The Doctor integrated the finer points Jung's therapeutic techniques with the techniques of Amanin of Betazed to create his own approach to reconstructing the memory of Seven of Nine. (VOY: "Retrospect")
Background information
Although not stated or referenced in dialog, the "racial subconscious" theory central to the plot of TOS: "Catspaw" is mostly based on Jung's work.