Marcus Loew was a serial entrepreneur who would go on to make a big name for himself in the motion picture industry. He started his journey building arcades and failed quite soon. He then got into the business of running Nickelodeons, which would charge a nickel (5 cents) to watch a short film. He converted this into a movie theatre and started building a chain. He would go on to partner with Adolph Zukor, who would found Paramount Pictures.
Marcus hired an enterprising advertising manager by the name of Nils Granlund as the advertising manager of Leow’s Theatres. In 1913, he spliced together rehearsal footage of The Pleasure Seekers into a montage that trialled after the show.
From the very beginning, "trailers" had always referred to a preview of a future movie release, but it made more sense back then because they were shown at the end of a movie screening, trailing the actual shown movie, instead of at the start, as is the practice today.
By the end of the 1930s, however, film studios realised that trailers would have a greater impact if they were screened before a movie rather than afterwards. Consequently, they began showing them in that order instead.
You’ve misspelled Marcus Loew’s name as LEOW. If you’re writing about history, please get your subject’s name correct.
https://en.m.wikipedia.org/wiki/Marcus_Loew