Gatchaman: The Series That Inspired Sentai
Honestly I really can only remember Ken as the leader, Joe the second-in-command, Jun the woman, Jinpei the kid and Ryu the fat guy. Actually the name Ryu wasn't always given to a leader figure at first.
This was their first flying fortress known as God Phoenix. When it got destroyed, it was rebuilt into...
New God Phoenix which is even more powerful than the last one...
Eventually the odd-looking Gatchaspartan was a result of combining five machinery into one powerful battheship for Gatchaman Fighter.
Sosai X was the leader of the Gallactor. He is a mysterious lifeform that seeks to devour worlds to gain ultimate power. Towards the third season, he was finally defeated by the Gatchamen with their Gatchaspartan which combined all five vehicles to one mothership.
The series itself did not yet feature human-sized monsters but at occasion, there were giant robot beasts that the Gallactor deployed their highest commanders from each season. They are:
Berg Katse who was the first common enemy. He had a great hatred for Gatcha Hawk. Later it is discovered he is also a she, being a fusion of fraternal twins created by the evil supernatural being Berg Katse. He committed suicide out of insanity. So far Super Sentai only had one hermaphrodite villain which was later in Gaoranger namely Rasetsu the Prince/Princess of Destruction. He was a joke character much later.
This was Gel-Sadora who was forced grown. In the end, she ended up attacking her master for killing her mother. She was killed by Sosai X. She somewhat became the inspiration for Jetman's Maria and the Jetman's non-canon Manga character only Ruma.
And this is Count Egobossler, certainly the most evil and sadistic of all the commanders who took over the nation by force and empowered by Sosai Z- and he's a pretty evil character that even Sosai Z couldn't match his personality. He was given tremendous power. He however planned to take over the throne of Sosai Z and gain power for himself, in which in the end he died. His facial characteristics seemingly inspired Radiguet of Jetman as well as his personality but to a much more evil scale.