Kikaider 01 (1973)

The noted robotics expert Dr. Kohmyoji created a powerful android to protect Japan from evil forces. When Hakaider starts his own evil organization, Dr. Kohmyoji’s android, Kikaider 01, awakens to fight Hakaider.
Hakaider has three assistants, Red Hakaider, Blue Hakaider, and Silver Hakaider. Together, they devise various schemes to cause destruction, but Kikaider 01 stops them all. Kikaider appears to assist Kikaider 01. Their chief goal is to capture a young boy, named Akira.
After Hakaider’s attempts fail, a new, mysterious character appears, Shadow Knight. Shadow Knight is a member of a competing, evil organization, SHADOW. When SHADOW proved to be more powerful than Hakaider, Hakaider unwillingly becomes a member of SHADOW.
It was later revealed that Hakaider has the brain of Professor Gill (also from the Kikaider TV series) within him. Professor Gill had designed a powerful robot and had tattooed the plans onto his two sons: Akira and his brother Hiroshi. Throughout the series, SHADOW helps Gill in building his robot, and Kikaider 01’s fight to stop them.