Ghidorah arrives!
Godzilla joins two others
Everything changes

The first four Godzilla movies had Godzilla squarely in the antagonist column. At best, he was an unstoppable force of nature. At worst, he was a metaphor for the atomic bomb. In any case, this was the one where Toho really established their shared universe by bringing Godzilla, Mothra, and Rodan to fight a threat none of them could handle alone. Things would never be the same for the franchise again.