Dynamic Superobot Wars

One of the first Super Robot manga and the one that introduced most of the traits of the Mecha genre. Constructed with the Super-Alloy Z, Mazinger was built by Professor Juzo Kabuto as a weapon against the Mechanical Beasts of the evil Dr. Hell. Koji Kabuto, the grandson of Professor Kabuto, becomes the pilot of Mazinger Z when his grandfather is killed, and battles from there on against Dr. Hell and his allies. This is the first series that introduced the concept of a pilot inside a Mecha, which all series from then on have followed.

The first Getter Robo series chronologically. Published 15 years before the rest of the manga, Getter Robo pioneered the idea of the combining and transforming robot. 

Millions of years ago, the dinosaurs were driven deep underground due to the sudden arrival of "Getter Rays" on Earth. After evolving into sentient beings, they grew bitter and vengeful at the humans who replaced them on the surface and began plotting their attack on humanity. 

Fighting against them is Getter Robo, a machine built by Professor Saotome which uses the mysterious Getter Rays as its power source. Piloting it are three strong-willed young men - the violent martial artist Nagare Ryoma, the psychopathic yet highly intelligent revolutionary Jin Hayato, and the hot-blooded Judo master Tomoe Musashi. Each controls one of three specially designed combat jets which can be combined together in different forms to form three different kinds of giant robots: the flying, axe-wielding Getter-1, the quick, drill-wielding Getter-2, and the tough, tank-like Getter-3.

After Emperor Gore and the Reptilian empire is defeated, a new enemy, Emperor Burai and his Hyakki empire rises and threatens to take over Earth. Ryoma, Hayato, and newcomer Benkei pilot the new Getter Robo G to save Earth. 

(Source: Anime News Network)

A short manga version of the UFO Robo Grendizer anime. Released along the anime series, UFO Robot Grendizer follows the adventures of Duke Fleed, the Prince of Planet Fleed, whom disguised as Daisuke, a farm worker, fights against the forces that destroyed his planet, the Vegan Empire, also the creators of Grendizer that Duke stole to fight them. While not originaly considered part of the Mazinger series, Koji Kabuto and the Mazinger mechas appear in this series, making it sort of a sequel. Grendizer introduced the concept of a transformable Robot and a space Mecha, concepts that were later taken into other mecha series. It was extremely popular in Japan, Canada, France, Italy and the Arab World and has a strong following in those countries even today.

The story tells about Hiroshi Shiba, a car racer who is mortally wounded on a laboratory accident, but restored to life by his father, Professor Shiba, a talented scientist/archeologist, who is incidentally investigating the relics of the ancient Yamatai Kingdom. The professor discovers a tiny bronze bell with sorcerous powers, and shortly afterwards he is murdered by the henchmen of Queen Himika, the ruler of the Yamatai (sometimes translated as Jamatai) Kingdom, who wants to seize the ancient bell and its power.