In 2369 he was mediating a dispute in the Rekag star system. He used empathic powers to become the perfect mediator by keeping his mind clear by transferring his negative emotions to others, somewhat akin to the fictional effects that a vampire character of Earth literature and stories has on its victims. This transfer caused the victims to become mentally unstable and age rapidly.
When his prime vessel Sev Maylor died- he had introduced her as his mother to explain her presence with him, although she was really a thirty-year-old woman-, he turned to Deanna Troi to serve as his new receptacle to transfer his negative emotions to. When his actions were discovered by Troi's shipmates, Alkar displayed no remorse and justified his actions by pointing out the services he performed for others as a mediator, forcing Captain Picard and Worf to leave the planet while he continued his work.
In an attempt to save Troi's life, Dr. Crusher was able to place her in a death-like coma, forcing Alkar to seek another person. He tried to use his aide Liva, but as Alkar was preparing to transfer his negative energy, Picard beamed Liva away. Alkar was left with his own negative energy. Overburdened by the emotions that he had long denied to himself, he aged rapidly and died in a few moments. (TNG: "Man of the People")