The Hays Code was a set of rules implemented in Hollywood from 1930-1968. This was a form of controlling what could and couldn't be shown in films, and included censorship of queerness amongst other things. Depending on how well those rules were followed, the movie could or couldn’t be shown in theatres. Today we realize how problematic this code is, but at the time it was widely accepted by most everyone. It is known for is having a damaging effect on the queer film industry. Whether it outright prevented a gay relationship to be shown, having the queer relationship tear the two characters’ lives apart leading to eventual death, or having LGBTQ+ people be the butt of every joke, it put queer representation in film behind by ten-fold. 

Today it still affects the industry with after-effects in the rating given to a movie (PG, R, MC-17, etc.) or helped foster film censorship in other areas like China. This overall prevents bigger industries like Disney and Marvel, to have good queer representation.