The Collaborative International Dictionary of English v.0.48:
Lothario \Lo*tha"ri*o\, n. [Name of a character in Rowe's drama, "The Fair Penitent."] A gay seducer of women; a libertine. [1913 Webster]WordNet (r) 3.0 (2006):
Lothario n 1: a successful womanizer; a man who behaves selfishly in his sexual relationships with women