He was portrayed by Chip Lucia.
At some point in his life, Alkar found he had the ability to channel all his negative thoughts and feelings into others. While it was beneficial to him, it was far less beneficial to those who were forced to take his psychic garbage. These unfortunate people underwent drastic negative personality changes, became sexually aggressive, and aged rapidly. Alkar ideally targeted other Lumerians since all members of the species had some degree of telepathic ability, but he found he could use other telepathic races as well as receptacles, as he called them.
The USS Enterprise (NCC-1701-D) first encountered Alkar when the unarmed transport he was traveling on to negoiate a cease fire on the planet Rekag was attacked. The Enterprise chased off the aggressors. Beaming aboard with his receptacle Sev Malor - who he introduced as his mother - he met Deanna Troi. Troi liked him but was put off by his mother, scared of the negative feelings she was getting from Malor. Starfleet decided it was a bad idea to have a diplomat go there in an unarmed transport. Alkar acquiesced and traveled as a guest on the Enterprise. He and Troi struck up a friendship, with Alkar requesting she assist him when they reached Rekag subject to Captain Jean-Luc Picard's approval.
A short time later Malor died. Asking Counselor Troi to join him in a Lumerian funeral meditation he was able to establish a new mental link to her, and began flooding her with negative thoughts and feelings.
Within a few days Troi's personality changes became apparent. Now Alkar refused to have her accompany him to Rekag. By now appearing as an older woman she went to the transporter room, horrifying Captain Picard with her appearance. She tried to attack Alkar, stabbing Captain Picard in the attempt.
After noting similar neurotransmitter levels in both Sev Malor and Troi Picard gave Doctor Crusher permission to perform an autopsy on Sev Malor even though Alkar had previously vetoed such an examination. The results were shocking - not only was Malor's organs those of a 30 year old woman, but DNA comparisons showed the two were not related.
Armed with this information Picard confronted Alkar on the surface of Rekag. Rekag told him about the psychic link. Disgusted Picard demanded he beam back on board to release Troi, but Alkar made it clear he would never do so. Armed guards under the employ of Alkar disarmed Worf and escorted the two out of the conference center before they could force Alkar to return.
Knowing that Alkar would never release Troi as long as she was a suitable receptacle for him, Doctor Crusher put Troi into a death like state. This caused Alkar to immediately turn to Liva to be his next receptacle. During the funeral meditation Crusher revived Troi. All the negative thoughts and feelings flooded back in to Alkar with a vengance. The Enterprise crew beamed Liva out of Alkar's quarters before he could harm her.
Meanwhile Alkar began rapidly aging, at a far greater rate than any of his receptacles ever had. When Lieutenant Worf arrived to arrest Alkar, he and his team found a very elderly Alkar who could only raise a finger in Worf's direction before collapsing and dying.
Troi completely recovered from her experience. William Riker told her that Crusher thought Alkar had been hit with negative thoughts and feelings at a sensitive time in the process of establishing the telepathic link, and having all of those negative thoughts and feelings flooding in to him overwhelmed him.