Transformable robots was a popular topic that is not only in Transformers, but are also in many Japanese animes such as Mobile Suit Gundam and Macross. The topic was also popular in many South Korean animes (a.k.a. manhwa) from the 1970s onwards. I'm going to review five of these movies for the sake of this article.
#5: Super Mazinger 3 (슈퍼 마징가 3) (1982)
Super Mazinger 3, released in 1982, was one of the many South Korean films that were not only derivative of Japan's Mazinger Z, but also Mobile Suit Gundam. The protagonist mecha almost looks like the RX-178 Gundam, except that it also features similarities borrowed from that of the Mazinger robot. The robot also transforms into a jet plane-type vehicle.
#4: Super Titan 15 (슈퍼 타이탄 15) (1983)
This movie features robots that don't necessarily transform, but they disassemble and reassemble in a way similar to that of Voltron, but I guess that could also count as a transformation (the Brazilian Transformers mockbuster Gladiformers did the same thing with the robots, as if it was a challenge for the animators to get them to actually transform). It also features what appears to be a railroad engine flying through space. You could mostly see that sequence at the beginning of the movie.
#3: Space Gundam V (스페이스 건담 V) (1983)
1983's Space Gundam V was a very infamous television series that is not exactly related to Mobile Suit Gundam despite its name. However, what made the show notorious was that the protagonist mecha was an unlicensed version of the VF-1J Valkyrie from the Macross franchise. Note that the same mecha was also used for the 1980s American TV show Robotech, which would have an upcoming movie pretty soon.
#2: Super Express Mazinger 7 (슈퍼 특급 마진가 7) (1983)
Super Express Mazinger 7 was a sequel to Super Mazinger 3, and this time the protagonist mecha looks a heck of a lot better, looking mostly like the RX-178 Gundam, and it still can transform, this time into a galactic express train. I've seen the first 7 minutes of it, and I wasn't able to watch the full thing because it kept on pausing on me (I watched a copy of it on YouTube). Still, the robot looks pretty cool. There was also a toy made to accompany the movie, too.
#1: Phoenix-bot Phoenix King (불사조 로보트 피닉스킹) (1984)
In 1984, Japan unleashed the Diaclone toy line, which would be the precursor to Transformers itself. In response to Diaclone's ensuing popularity, a group of South Korean animators unleashed Phoenix-bot Phoenix King. Its protagonist mecha was derivative of that of the Diaclone No. 11 fire engine, except that it gets its powers from a legendary phoenix, hence the name. It was distributed by Hong Kong filmmaker Joseph Lai in the United States and Europe, and was also dubbed into English, given the title Defenders of Space. I also did a full review for this movie, so feel free to check it out.