Go Nagai's legendary manga, Devilman, came out in June 1972, and it was such a huge instantaneous success that it became an anime after only a month of being in print. Devilman was Go Nagai's first anime work, in fact. This super-violent series was toned down greatly for the 70's anime version.
Trapped in the Earth's glacial ice are countless numbers of demons waiting for the day that they will be released and can rule the world once more. It is up to Akira Fudo and Ryo Asuka to stop these demons from world domination. However, it takes a demon to destroy a demon, so Ryo comes up with a plan to get the powers of a demon: the plan is to have a demon possess him. In search of the perfect location for finding demons, the pair ends up at a satanic nightclub. In order to attract the attention of demons, Ryo randomly kills people in the club as Akira watches in shock.
Before he knows it, Akira finds himself large and furry, with fangs and wings. Akira has been possessed by Amon, the lord of war. However, this mixture of man and demon retains Akira's heart and soul. Together, they are known as Devilman. Later in the series, Ryo is possessed by a demon as well, but not just any demon. It is the Lord of Darkness himself, Satan! With the genitals of a man and the upper body of a woman, Satan is Devilman's rival for the rest of the series, right up until Armageddon. They amass armies of demons (Satan) and devilmen (Devilman), respectively.
Devilman was later remade into a 2-volume OAV series, and it is now commercially available from Manga Entertainment. There was also a sequel to this series called Devilman Lady that aired on Japanese television in 1998. Tied to the same universe are series such as Cutey Honey, Violence Jack, and (very amusingly) Kekko Kamen. Violence Jack is especially amusing, since characters from just about all of Go Nagai's works make an appearance in this manga series.
Shortly after the Devilman manga was released, Go Nagai made the revolutionary giant robot manga, Mazinger Z. Also wildly popular, it became an anime, as well, within the year. It began airing on Fuji TV in December 1972, becoming the first "true" super-robot anime ever. The immense popularity of Mazinger Z inspired Go Nagai to produce more super-robot anime and manga such as Getter Robo and Getter Robo G, Groizer X, Kotsetsu Jeeg, Great Mazinger, UFO Robot Grendizer, and God Mazinger. Several other people got in on the new sensation, and Chodenji Robot Combattler V, Chodenji Machine Voltes V, Magne Robot Ga-kin, and many more were created. Indeed, the 1970's were saturated with super-robot series.
Mazinger Z is the guardian of Earth, always defending it against the non-stop attacks from outer space by Doctor Hell and his legion of robot monsters. Built out of Super Alloy Z by Professor Juzo Kabuto, Mazinger is piloted by the Professor's son, Koji Kabuto. Mazinger is made up of three main parts. The Over Pilder is a small flying vessel that holds the pilot, and it lands in the brain area of the main robot body. Of course, there's also the main body. The last piece would be the Jet Scrander, which is a jetpack-like vehicle that gives it flight ability.
To help Koji Kabuto in his battle against Doctor Hell, he is joined by his two friends, Sayaka Yumi and Boss, piloting the Aphrodite A and Boss Robot, respectively. The Aphrodite A is rather weak, and the Boss Robot has only humor value (it was made from scrap parts). Later in the TV series, the Aphrodite A gets upgraded to the Diana A. Mazinger employs a variety of special attacks: Photon Beam, Freeze Beam, Rust Hurricane, Drill Missile, Breast Fire (its most powerful attack), and (my favorite) Rocket Punch.
Mazinger Z was considered very innovative for its time. It was the first robot that was piloted. In addition, it introduced the concept of calling out the name of one's attacks. This aspect in particular leads to reader/viewer participation. When people are reading the manga or watching the anime, they enjoy calling out the name of the move with the character.
Because of Mazinger Z's great success, Go Nagai made the sequel, Great Mazinger, but it was not as successful as its predecessor. The giant robot show that followed it (in the same universe), UFO Robot Grendizer, was considered far superior.
Mazinger Z vs. Devilman is Go Nagai's first of several crossover movies. Movies that followed were Mazinger Z vs. Great General Dark, Great Mazinger vs. Getter Robo G, Great Mazinger vs. Getter Robo, and Grendizer vs. Great Mazinger.