Getter Robo

Getter Robo is a manga by the great Ken Ishikawa and his friend Go Nagai (creator of the also famous Mazinger Z), adapted into a television series that was more light-hearted than the more horrific and psychotic manga, the closest animated show to the original is the New Getter Robo OVA which combines elements of the original manga with the sequel manga, Shin Getter Robo.

Getter Robo (TV)
Television series loosely based on the manga, the personalities of the protagonists for example are toned down from psychotic to just hot-blooded.

Getter Robo G
Direct sequel to Getter Robo featuring a new robot and a new pilot; Benkei Kuruma.

Getter Robo Go
New robot Getter Robo Go, powered by Plasma energy because Getter Rays were considered too dangerous due to Getter Robo and Shin Getter Robo (a very powerful incarnation).

Getter Robo Go (TV)
Re-imagining of the original television series with Getter Robo Go characters and robots.

Getter Robo Armageddon
OVA loosely based on the Shin Getter Robo Manga, it does retain a darker tone than previous animated adaptations.

Shin Getter Robo vs Neo Getter Robo
OVA looseley based on the Getter Robo Go and Shin Getter Robo manga, returns to the tone of the 70s television series.

New Getter Robo
OVA based on the original Getter Robo manga with elements of Japanese mythology and the Shin Getter Robo manga, the most faithful adaptation of the original manga to date.

Other Wikis
http://gonagai.wikia.com/wiki/Go_Nagai_wiki