Green’s Dictionary of Slang

a libertine, a rake.

[1703		N. Rowe Fair Penitent Vi: Is this that Haughty, Gallant, Gay Lothario].
1748		Smollett Roderick Random (1979) 122: When I demanded admission to Lothario (so let me call him) I was desired to send up my name and business.
1756		World No. 202 n.p.: Proud of the summons to display his might, The gay Lothario dresses for a fight [F&H].
a.1800		W. Cowper Hope in Works (1866) 84: Lothario cries, ‘What philosophic stuff.’.
1818		‘Thomas Brown’ Fudge Family in Paris letter VIII 87: Some, who’re Lotharios in eating, should wish / Just to flirt with a luncheon.
1824		T.E. Hook Merton in Sayings and Doings 1st Ser. II 285: The elegant, ‘gallant, gay, Lothario,’ [....] was no other than Sir Harry Lavington, a baronet, a lancer, and a lady-killer.
1830		Lytton Paul Clifford II 96: Our present design of setting up the gay Lothario, and trying our chances at Bath for an heiress.
1845		Bell’s Life in Sydney 6 Sept. 2/4: Mr. John Willis, a valetudinarian Lothario, whose age and infirmities should have proved a better safeguard against the fascinations of the frail sisterhood.
1849		Lytton Caxtons III Pt xviii 278: No woman could have been more flattered and courted by Lotharios and lady-killers than Lady Castelton has been.
1858		A. Mayhew Paved with Gold 179: Which terms [...] were intended to refer to the gay Lothario’s usual gallantry and great affection for the female sex.
1864, 1867, 1870		Hotten Sl. Dict.
1876		Times 2 Nov. n.p.: Maurice, a most inflammable Lothario, catches fire at her charms [F&H].
1895		C. Crowe Aus. Sl. Dict. 46: Lothario, a heartless villain.
1898		Binstead & Wells Pink ’Un and Pelican 20: The Manchester Lothario had got twenty pounds on Barcaldine with the ‘Nanty Poloney Ironclad Firm’.
1903		‘Hugh McHugh’ Out for the Coin 47: Mrs. John, your husband’s gay Lothario.
1916		J. Lait ‘Heritage of the Suffering Brother’ in Beef, Iron and Wine (1917) 203: Jack wasn’t much of a Lothario. He mostly looked sheepishly at her and blushed.
1926		Wood & Goddard Dict. Amer. Sl.
1927		E. Wallace Squeaker (1950) 16: He seems to have an idea that you’re a gay Lothario, my boy!
1934		(con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 211: This Lothario, Haggerty, better be early to bed.
1946		in G. Legman Limerick (1953) 16: There was a gay dog from Ontario / Who fancied himself as a Lothario.
1979		‘Iceberg Slim’ Airtight Willie and Me 138: Casper, the elderly and notorious bisexual Lothario.
1989		T. Blacker Fixx 8: Jonty Fixx, bold-eyed lothario and despoiler of virgins.