Dann Lendann was a male Luss with orange skin and pointed ears. In 2368 he was an aide to the Ambassador of the Luss. He and the Ambassador were attending the Sindareen peace talks on the USS Enterprise when he reunited with his old friend, Counselor Deanna Troi.
Commander William T. Riker was embarrassed when he walked in on Dann and Deanna in bed together in her quarters. Later, Riker arranged for Dann to be seated next to Deanna at the peace talks. Dann and Deanna left the talks together with his arm around her waist.
In the year 2408, Mar Loc, a Sindareen scientist, used the Guardian of Forever to travel back in time and poison Deanna at the conference. In an alternate timeline, she died that evening in her quarters while Dann was helpless to prevent it.
In "the correct" timeline, Dann was actually knocked out and replaced by a time-traveling Chameloid, Lieutenant Blair, sometime between the conference and his meeting with Deanna in her quarters. (TNG novel: Imzadi)