The noun teetotaler—reportedly coined in 1833 by an English abstinence advocate—means one who abstains completely from alcohol beverages. The single-l spelling, teetotaler, is preferred in American English. Teetotaller, with two l‘s, is the usual form in the main varieties of English used outside the U.S..
Teetotal is the corresponding verb, and teetotalism (in both American and British English) is the practice of abstaining from alcohol.
Examples
U.S.
Trump, known as much for his reality shows The Apprentice and Celebrity Apprentice as he is for his business acumen, is a teetotaler. [Forbes]
It’s also bad news for teetotaler Christians who hope to inflict their brand of religion on the rest of us god-fearing folk who see nothing wrong with having an occasional beer. [Savannah Morning News]
U.K.
Or Edith, a strict teetotaller, announcing her distaste at the goings-on at the village inn. [Telegraph]
Were he a footballer and not exposed to the rigours of rugby on a weekly basis, the teetotaller would be a good bet to play into his 40s. [Scotsman]