a·las·tor also A·las·tor 
(ə-lăstər, -tôr′)
(ə-lăstər, -tôr′)n.
An avenging deity or spirit, the masculine personification of Nemesis, frequently evoked in Greek tragedy.
[Greek alastōr, from alastos, unforgettable : a-, not; see A-1 + lanthanein, lath-, to escape notice.]