Well, Wikipedia claims
that the 1949-55 series Captain Video
featured a robot named I TOBOR as "an important, semi-regular character," but that's an exaggeration, since it only appeared in a few episodes
. So I don't think that counts as making regular appearances.
Astro from Tom Corbett
, a human born on Venus, has already been mentioned, but he would only count as an alien culturally rather than biologically. There was a Flash Gordon
TV series in 1954-5, so I was thinking maybe it might've had Ming and Aura as regulars, but instead it just had Flash, Dale, and Zarkov on various far-future space adventures. They visited lots of alien planets, but no aliens made regular appearances as far as I can tell.
Ahh, wait, here we go! In 1954's Rocky Jones, Space Ranger
, the main recurring antagonist was Queen Cleolanta or Cleolanthe (Patsy Parsons), ruler of the planet Ophiuchius. Her earliest listed appearance on IMDb is April 10, 1954.
I found another couple of puppet aliens, Johnny Jupiter
and his compatriots, from a 1953-4 kids' show. As the name suggests, they were from Jupiter.
Still, I think the prize for first regular TV alien goes to George Reeves as Superman, beginning in September 1952.
Meanwhile, over in Japan in 1963, we've got a couple of famous cases of dead people being resurrected as androids, namely Mighty Atom (Astro Boy) and 8 Man. Plus various other aliens in '60s anime such as Tezuka's The Amazing 3
So a list of regular or recurring nonhuman characters in science fiction television prior to Star Trek
would look something like this (limiting it to sentient aliens and robots):
Sep. 1952: Kal El/Clark Kent/Superman (The Adventures of Superman
Mar. 1953: Johnny Jupiter et al. (Johnny Jupiter
Apr. 1954: Queen Cleolanta (Rocky Jones, Space Ranger
Jul. 1959: Mr. Squiggle (Mr. Squiggle
Sep. 1962: Rosie (The Jetsons
Oct. 1962: Robert the Robot (Fireball XL5
Jan. 1963: Mighty Atom/Astro Boy (Tetsuwan Atomu/Astro Boy
Sep. 1963: Uncle Martin (My Favorite Martian
Nov. 1963: 8 Man (Eitoman
Nov. 1963: The Doctor (Doctor Who
Sep. 1964: AF709/Rhoda Miller (My Living Doll
Feb. 1965: Adam Suisse (The Stranger
May 1965: Space Ace (Uchuu Esu/Space Ace
Jun. 1965: Popi (Planet Boy Popi/Prince Planet
Jun. 1965: Bokko, Nokko, and Pukko (The Amazing 3
Sep. 1965: Robot B-9 (Lost in Space
Jul. 1966: Ultraman (Ultraman
This is probably not an exhaustive list, but it's clear that Spock was a latecomer.