Troi was born to Betazoid mother Lwaxana and a human father, Lt. Ian Andrew Troi, a Starfleet officer. Her father died when she was very young. She had a sister Kestra, who died at the age of six in an accident several months after Deanna was born. Being half betazoid, Deanna is an empath. She is a highly trained psychologist and Starfleet officer, with strong diplomatic skills. She loves chocolate and enjoys playing poker with her crewmates. While attending the University of Betazed, she met Ensign William Riker, and they became romantically involved. They parted when Riker was posted to the U.S.S. Potemkin. They would later both serve on the U.S.S. Enterprise-D together. She bore a child, Ian Andrew Troi, involuntarily conceived with an unknown non-corporeal life, in 2365. When the child found out it was endangering the ship, it returned to its non-corporeal form and left.

Starfleet History
2355-2359 Attended Starfleet Academy
2360-2363 University of Betazed, advanced career study in Psychology
2364 Posted to U.S.S. Enterprise NCC-1701-D Ship's Counselor. Promoted to Lt. Cmdr.
2369 Abducted by Romulan underground and surgically altered to appear Romulan to assist in defection of Romulan pro-counsel M'ret to the Federation.
2370 Passed Bridge Officer's Exam and promoted to Commander.
2371 U.S.S. Enterprise NCC-1701-D was destroyed at Veridian III.
2372 Posted to Sovereign-class U.S.S. Enterprise NCC-1701-E.
2373 U.S.S. Enterprise NCC-1701-E succeeded in stopping the Borg's temporal incursion. Assisted in rebuilding Zefram Cochrane's warp ship, The Phoenix. Commanded mission control.

Deanna Troi was first seen in "Encounter at Farpoint" (TNG).