Lothario is a male first name which came to connote an unscrupulous seducer of women.
In The Impertinent Curiosity, a story-within-the-story in Don Quixote (c. 1605), by Miguel de Cervantes

Miguel de Cervantes

Miguel de Cervantes Saavedra was a Spanish novelist, poet, and playwright. His magnum opus, Don Quixote, considered the first modern novel, is a classic of Western literature, and is regarded amongst the best works of fiction ever written...

, a man named Anselmo coerces Lothario, his faithful friend, to test the virtue of Anselmo's wife, Camila. Though Lothario sincerely attempts dissuading Anselmo from testing his wife's fidelity, the friend insists, and Lothario eventually falls in love with Camila.

Lothario is also a character in the play The Fair Penitent

The Fair Penitent

The Fair Penitent is Nicholas Rowe's stage adaptation of the tragedy The Fatal Dowry, the Philip Massinger and Nathan Field collaboration first published in 1632...

(1703), by Nicholas Rowe

Nicholas Rowe (dramatist)

Nicholas Rowe , English dramatist, poet and miscellaneous writer, was appointed Poet Laureate in 1715.-Life:...

. In the play, Lothario seduces and betrays Calista.

Through the Rowe play, the eponym

Eponym

An eponym is the name of a person or thing, whether real or fictitious, after which a particular place, tribe, era, discovery, or other item is named or thought to be named...

 a lothario, came to mean a handsome, seductive ladies' man. It was often prefixed with "gay", from Rowe's line, "haughty gallant gay Lothario". A "gay lothario" was an amoral seducer.