The Titan Avatar, known by the crew as simply Titan, or more commonly as the Avatar, was the sentient consciousness that arose from the USS Titan's computer. The avatar recognized the authority of Captain Riker and for a brief time, served as a member of the ship's crew. The holographic form she chose to represent herself was that of Minuet, much to Riker's dismay. (TTN novel: Synthesis)
As of 2381, a semblance of a consciousness had already begun to arise within the ship's computer. It was a partially formed entity. When the Sentry known as SecondGen White-Blue was forced to momentarily take control of Titan's computers, he became aware of the partial consciousness and gave it the option to become a full sentient being. It took the offer.
Although she felt a connection and a duty to her crew, they at first felt somewhat distrustful of her. She looked up to Xin Ra-Havreii as a father, although he was hesitant to return those feelings. She also hoped to win Captain Riker's respect. She did, however, become friends with Ensign Torvig Bu-Kar-Nguv, who identified with her. She was able to help the crew during their interactions with the Sentries and the Null. (TTN novel: Synthesis)
The Avatar sacrificed herself to end the threat of the Null, saving both the Titan and the Sentry civilization. She sewed closed the ruptures in subspace created by the Sentry engines that had allowed the Null to slip through from subspace in the first place. She was then trapped in subspace, and presumed to have died there. (TTN novel: Synthesis)