The show lasted from 1989 to 1999, with an astonishing ten seasons, and a new season in the works.
After a successful season 1, Comedy Central sent a box of films to the Best Brains office where MST3K, as fans call it, is produced. Included in the film package was Godzilla vs The Sea Monster, the first time an Eiji Tsuburaya film was "riffed" on the show.
After season two's finale of Godzilla vs the Sea Monster, the Best Brains did an odd move, an American produced movie followed by a Japanese movie. This was the season that had the most Tokusatsu related 'experiments'. Most noteably, this was the season of Gamera films. But sprinkled between the Gamera films, some Tsuburaya Productions, dubbed and re-edited by Sandy Frank, made the cut, including 1974's Saru no Gundan retitled as 'Time of Apes', a 26 episode series riding on the coat tails of the then broadcasted in Japan for the first time, 'Planet of the Apes'. It was cut down in size to make a movie and dubbed into English.
Another Tsuburaya epic that was given the Riff treatement, was the 1978 Sci-fi special effects show, StarWolf here, retitled as Fugitive Alien. Again, like Saru no Gundan, the original tv airing was 26 episodes smashed together for one film. But, an MST3K first, the movie was too long and 'produced' a sequel, 'Star Force: Fugitive Alien 2'.
They also riffed the made for tv movie of Mighty Jack.
Fast forward to Season 10, when original captive, Joel Robinson, played by Joel Hodgeson, escaped the clutches of Dr. Clayton Forrester, played by Trace Bealiu, and TV's Frank, played by Frank Coniff, and replaced almost instantly with Mike Nelson, played by comedian and head writer since season 2, Michael J. Nelson. Behind the scenes, other changes where made, Frank left the show and was replaced by Mary Jo Phel's character, Pearl Forrester, for season 7, and then Trace left, being replaced by Mary since season 8. Bill Corbette, a play wright and a comedian, took over for Crow T. Robot who Trace played since the original KTMA run. The show was then given a home at SciFi, now named Syfy, after it's run on Comedy Central ended.
Now, while no direct mention or film of Tsuburaya Production Inc where 'riffed', The☆Ultraman did make a surprise appearance in the season 10 episode of Merlin's Shop of Mystical Wonders.
Mystery Science Theater Hour Wraps
Comedy Central, the original channel that took the show in, got complaints that the show was 'too long'. So Best Brains made 'Mystery Science Theater Hour', splitting a single two hour show into an hour. Hosted by Jack Perkins, played by Michael J. Nelson, he would recap the story and movie for the audience. In one episode, the season 3's Gamera vs Guiron, an Ultraseven Kaiju made a surprise appearance, the Greyon Monster, filling in for Gyaos. It was a figure of Greyon made for the Godzilla and Friends toyline. The segement ended with Jack and his assiosiate producer playing baseball with Guiron's blade and Greyon.