What was the first monster to appear alongside Godzilla?

Anguirus was the first monster to appear alongside Godzilla. Introduced in the 1955 film "Godzilla Raids Again," Anguirus is an ankylosaurus-like creature that engages in a fierce battle with Godzilla. This iconic duel marked the beginning of a long-running tradition of Godzilla facing off against other monstrous adversaries, establishing Anguirus as the first kaiju to stand against the King of the Monsters and establishing the franchise's beloved tradition of epic monster battles.