https://www.cnet.com/news/avengers-4-trailer-hype-had-you-just-where-marvel-wanted-you/

Hype for a movie is one thing. But hype for a trailer? This is where we are now -- and it all began more than a hundred years ago...

The first-ever trailer was shown in a New York Loews cinema way back in 1913, and it wasn't even for a movie. Instead, it was a short film made to advertise the Broadway musical The Pleasure Seekers. But it was a brilliant hook: Tease entertainment seekers with a preview of another piece of entertainment they might enjoy. Naturally, the promotional films took off.