Anastasia Trexler is Len Trexler's deceased wife. She was a tall brunette that Malory refers to as "the crazy one." She killed herself leaving Trexler a widower. Trexler does not seem very broken up about her passing.
Anastasia could be the same person as Ruth Anne Litzenberger, because Sterling Archer might not have known her real name and thus dreamed up another one in Once Bitten, which would increase the probability for Len being Sterling's real father, according to the further events in Archer's flashback.