Godzilla's appearance gradually changed throughout the early 1960s and mid-1970s. From top-left to bottom-right, Top left King Kong vs. Godzilla (1962), Top right Ebirah, Horror of the Deep (1966), Bottom left Godzilla's Revenge (1969), and Bottom right Godzilla vs. Mechagodzilla (1974)
As alluded to at the end of the original movie, Godzilla again surfaced at first as a menace in Godzilla Raids Again (shown in the U.S.A. as Gigantis, The Fire Monster, In which Godzilla is refurred to as Gigantis and Anguirus as Angurous or Angurousaurus). Setting the tone for future Showa-series films, Godzilla's fate is uncertain at the end. His next film was 1962's King Kong vs Godzilla.
The menacing ego of Godzilla's final film in the Showa series was 1964's Godzilla vs.The Thing (that being the original American release title, but since known by the Japanese and international title, Mothra vs. Godzilla).
Starting with Ghidorah, the Three-Headed Monster, Godzilla took on the "good guy" persona he would wear for the remainder of the series. He would team up with Mothra, Rodan, and Anguirus along with other monsters to battle a variety of foes both mundane (Ebirah, Kumonga, and Kamacuras) and bizarre (Hedorah, Gigan, and Megalon). He even gained a son in the form of Minilla.
The series ended with Terror of Mechagodzilla in 1975. The final scene depicted Godzilla wading off into the sea, not to be seen until his return in the VS series ten years later. It is notable, however, that the earlier-released film Destroy All Monsters took place in 1999, twenty-four years after Terror of Mechagodzilla. The series could also be said to truly end with Destroy All Monsters's ending, which depicted all of Earth's monsters living out the rest of their days in peace on MonsterIsland. This "jump" of dates also explains how King Ghidorah appeared in movies such as Godzilla vs. Gigan after he was killed in the earlier film.
The Toho sentai series Zone Fighter is notable in that it features Toho Kaiju from the films, such as Gigan, King Ghidorah and Godzilla himself. Produced during the 70s, Toho has gone on record stating that the events depicted in the Zone Fighter television series are part of the Showa era, taking place between Godzilla vs. Megalon and Godzilla vs. Mechagodzilla.
History of Godzilla