Helping give rise to the genre of mecha (giant robot) anime, such as Gundam and Voltes V, Mazinger Z was the earliest major incarnation of heroes piloting large robots to fight evildoers and save people.
Though preceded by robot-themed anime before it, the most popular being Astro Boy, its basis as a superhero show was unique and fresh at the time. Its title as a "super robot Mazinger-Z" is even sung in its theme song, and the show itself takes inspiration from Japanese sci-fi that gave rise to giant monsters such as Gojira (Godzilla), with the protagonist fighting ancient mechanical monsters.
The show's predecessor, Tetsujin28-go, was the first giant robot anime to become popular with audiences, going on to directly inspire the creator of Mazinger-Z. The latter show, however, is the first to have a human pilot the mech, with Tetsujin28-go having the robot remote controlled.
Mazinger-Z as a super-mech is the template from which other world-saving mecha anime took inspiration, and though it's since been overshadowed by the internationally acclaimed Gundam franchise and the ever-lauded Evangelion, it's still remembered as the heroic progenitor of the super robot genre.