Sev Maylor was a Lumerian woman who accompanied Ves Alkar when he arrived on the USS Enterprise-D in 2369.
Alkar introduced Maylor as his mother, but in reality she was a female companion that he used to store his unpleasant and hateful thoughts in her mind, so his mind could remain pure, helping him mediate disputes. This caused rapid aging in the victim, followed by premature death. Maylor transported onto the Enterprise-D with him and immediately took a dislike to Deanna Troi and insulted her, believing Alkar would replace her with Troi. Shortly afterwards, Maylor died.
During the autopsy, Dr. Crusher determined that Maylor was not Alkar's mother, and that she was only thirty years old; Alkar had previously claimed that the woman was 93. This helped to uncover Alkar's horrible deed and save the life of Troi, who would have become his next victim. (TNG: "Man Of The People")