alastor (n.) Look up alastor at Dictionary.com
"relentless avenging spirit or deity, destroying angel," perhaps literally "the unforgetting," from privative prefix a- "not" (see a- (3)) + root of lathein "to forget," aorist of lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). Or else it might be connected with alaomai "to wander, roam," figuratively "to be distraught." As a proper name, in Greek tradition a son of Neleus and Chloris; brother of Nestor, he was slain by Herakles.