“Arena” was a story from 1944 where Earth was about to have an apocalyptic final war with a hideous, unseen alien race known as “the Outsiders.” On the eve of the titanic battle, advanced alien artificial intelligences teleport one human and one Outsider to a planet to fight it out, man to man, and the loser will have their entire battle fleet and planet destroyed. 

It was very common in the 60s to turn an award winning scifi short story into an episode of the Twilight Zone and the Outer Limits (as Ray Bradbury and Richard Matheson can attest), but “Arena” was adapted into an episode by none other than the famous Star Trek, in one of their most famous episodes (aka the one where Captain Kirk fights a big lizard by the famous Vazquez Rocks), with Frederic Brown paid and given an author credit on screen. This is one of the only times that Trek would adapt a non-Trek short story.