Groizer X is a mecha anime series with a few manga adaptations by Go Nagai and Gosaku Ōta. It was originally created as a side project by Nagai while working on Mazinger and became an anime in its own right in 1976.
Aliens hiding in the Arctic region called the Gaira had decided to conquer Earth. The scientist Dr. Yan and his daughter Rita were captured by them to build a super weapon in their effort. Dr. Yan completed the giant transforming super robot Groizer X. Rita managed to escape on the robot but crashed meeting the pilot Jo Kaisaka in the process. Together they fight against the Gaira with Groizer to save the Earth.
While not as popular as other Super Robot shows by Dynamic Productions, Groizer X did appear in other related media such as Dynamic Super Robots Soshingeki where it appeared with the other Dynamic robots including Psycho Armor Govarian. In Shin Mazinger Shogeki! Z Hen, a series of Mechanical Beasts were designed and named after Groizer.