Donald LeRoy LaFontaine (August 26, 1940 – September 1, 2008) was an American voice actor who recorded more than 5,000 film trailers and hundreds of thousands of television advertisements, network promotions, and video game trailers over four decades.

He became identified with the phrase "In a world ...", used in so many movie trailers that it became a humorous catchphrase. Widely known in the film industry, the man whose nicknames included "Thunder Throat", "The Voice of God" and "The King of Movie Trailers", became known to a wider audience through commercials for GEICO insurance and the Mega Millions lottery game.

LaFontaine was born on August 26, 1940, in Duluth, Minnesota, to Alfred and Ruby LaFontaine (née Dravland; b. 1918). LaFontaine said his voice cracked at age 13 in mid-sentence, giving him the bass tones that later brought him much fame and success. After graduating from Duluth Central High School in 1958, he enlisted in the U.S. Army and served as an audio engineer with the U.S. Army Band and the U.S. Army Chorus.

LaFontaine continued to work as a recording engineer after discharge and began working at the National Recording Studios in New York City, where, in 1962, he had the opportunity to work with producer Floyd Peterson on radio spots for Dr. Strangelove. Peterson incorporated many of LaFontaine's ideas for the spots and, in 1963, they went into business together producing advertising exclusively for the movie industry. LaFontaine claimed that this company first came up with many of the famous movie trailer catchphrases, including his own future signature phrase "In a world ...".

While working on the 1964 western Gunfighters of Casa Grande, LaFontaine had to fill in for an unavailable voice actor to have something to present to MGM. After MGM bought the spots, LaFontaine began a career as a voiceover artist.

He became the head of Kaleidoscope Films Ltd., a movie trailer production company, before starting his own company, Don LaFontaine Associates, in 1976. Shortly thereafter, he was hired by Paramount to do their trailers and was eventually promoted to vice president. He decided to get back into trailer work and left Paramount, moving to Los Angeles in 1981. LaFontaine was contacted by an agent who wanted to promote him for voiceover work, and from then on worked in voiceovers. At his peak, he voiced about 60 promotions a week, and sometimes as many as 35 in a single day. Once he established himself, most studios were willing to pay a high fee for his service. His income was in the millions.

LaFontaine often had jobs at several different studios each day. With the advent of ISDN technology, LaFontaine eventually built a recording studio in his Hollywood Hills home and began doing his work from home.

LaFontaine lent his distinctive voice to thousands of movie trailers during his career, spanning every genre from every major film studio, including The Cannon Group, for which he voiced one of their logos (he also voiced the Viacom closing logo in 1990, simply saying the company's name after it had been formed on the screen). For a time, LaFontaine had a near-monopoly on movie trailer voiceovers. Some notable trailers which LaFontaine highlighted in the intro on his official website include: Terminator 2: Judgment Day, Shrek, Friday the 13th, Law & Order and Batman Returns. LaFontaine stated in 2007 that his favorite work in a movie trailer was for the biographical film The Elephant Man, though according to a response to the question on his website, he had several trailers which stood out in his mind, and he didn't like to choose one.