Demelos was an Enaran Regressive.

During the "voluntary resettlement" in which the Regressives allegedly moved to a distant colony, Demelos resisted the authorities who were forcing him to leave. In the resulting struggle, Korenna Mirell received a gash on her cheek. (VOY: "Remember")

Demelos was played by regular extra Pablo Soriano in an uncredited role.
This character was murdered, according to the Star Trek Encyclopedia (4th ed., vol. 1, p. 201).