Science fiction and fantasy has been a staple of television since the early days of the medium and has generated many many shows over the past sixty-plus years. But as for which one was the very first sci fi TV entry, that is somewhat of a debate.
Way back in 1938, the BBC took an early stab at Science Fiction when they adapted a portion of Karel Čapek’s play R.U.R. aka Rossum’s Universal Robots, the literary work from which the term Robot was coined. So that would be the first television production in the genre. And then in 1946, after the BBC resumed production following WW II, they aired a full adaptation of R.U.R. for television. Later in the decade, the BBC also did an adaptation of the Time Machine by H.G. Wells. But neither of those count as an ongoing sci fi TV series.
The first show to make it to the air as a planned ongoing production would be Captain Video and His Video Rangers which ran on the now defunct DuMont network. That kiddie space opera–which set the template for sci fi shows that would follow in the 1950s–had its first broadcast on June 27, 1949. Then, less than one month later, the proto-Twilight Zone anthology series Lights Out bowed on NBC on July 19, 1949. However, that show, which was based on the popular radio series, actually had a four episode run as specials back in 1946, probably to promote the radio show. It was not intended to be a regular series at that time as far as I am aware, so the debate is whether you really count that as Season 1 (as IMDb does) or if you consider that just a one-off and give Captain Video the nod as the first sci fi TV series. You can say this for the latter at least: it was the first show in the genre to make it to the small screen as a planned continuing series even if Lights Out did beat it to television in a limited format by a few years. Captain Video was also the first straight science fiction series since Lights Out ventured into the supernatural, paranormal, and suspense.
An additional tidbit about early television programs: they were filmed live (making special effects a considerable challenge) and therefore many shows from the nascent years of the medium do not exist anywhere today in archival format. Thus, the early British sci fi productions as well as the first four episodes of Lights Out do not exist anymore. Some shows, though, were archived with kinescopes, a process where they would film a television airing the program. Much of the 1949 Lights Out series exists in this format. Captain Video’s run was recorded this way as well, but most of it was destroyed after DuMont went defunct (though a handful of episodes do still exist). A small number of shows in the early years of television eschewed recording live and chose to use film instead, such as Rocky Jones, Space Ranger, and their complete episode run is still available today.
