Jaan Devin was a Selelvian civilian who lived aboard the USS Enterprise (NCC-1701-D) in 2365, and suffered from the Selelvian disease known as "the Rot". During his time aboard the Enterprise he became friends with Wesley Crusher, nicknaming him "Orange".
Jaan's friendship with Wesley was less altruistic than it initially appeared, as when Jaan learned that he was dying, he--apparently unintentionally--used his Selelvian power of suggestion, known as "The Knack", to prompt Wesley to focus all his efforts into finding a cure for the Rot. This caused Wesley to go as far as to disregard all his other duties and move various computers into his quarters to increase the resources he could use. Even after Jaan realized what had happened, he allowed Wesley to continue his search on the grounds that he was what really "counted", theorizing that Wesley might pull it off, despite the fact that Wesley wasn't even allowing himself to sleep as he continued his efforts.
During a counseling session with Counselor Deanna Troi shortly after being diagnosed with the Rot, Jaan attempted to use the Knack to seduce her, making Troi seem to feel as if her clothes were becoming very uncomfortable. Before Jaan could go any further, his attempt was interrupted by Commander Riker, who was looking for Troi, so Jaan quickly planted in Troi's mind that he was fine emotionally as a cover for his actions.
When a Kreel named Aneel promised Jaan a cure for "the Rot"--claiming that they had found a medical database along with various advanced weapons that the Kreel had recently salvaged, the database including information on a disease similar to the Rot--Jaan betrayed his friends and colleagues in order to get the cure, helping the Kreel access the Enterprise armory. However, when he led Aneel to the bridge and disclosed his treachery to Captain Jean-Luc Picard and Counselor Troi, Aneel mockingly concluded that he would give Jaan the cure now and shot him with a phaser set to kill, reasoning that he wasn't even lying about possessing a cure as death cured everything. (TNG novel: Strike Zone)