Giant Octopus

Oodako is a giant octopus daikaiju that debuted in King Kong vs. Godzilla (1962) and returned in War of the Gargantuas (1966). He's also known as the Daidako (Giant Octopus) and The Giant Devilfish. He also appeared in an alternate ending for the movie "Frankenstein Vs. Baragon" (aka: "Frankenstein Conquers The World") (1965)

King Kong vs. Godzilla
One night Oodako crawled ashore on Farou Island and attacked a village hut in an attempt to get the special soma berry juice, that the natives stored there. The natives and the pharmaceutical company team attacked Oodako to stop it, but failed. Then King Kong appeared behind a giant wooden fence. He crumbled the fence with his bare hands and threw the pieces at Oodako. Kong grabed Oodako, but the octopus held tight on to Kong's head. There was a short struggle, but in the end, Kong pulled off the monster and threw it to the ground. Then he threw two boulders at Oodako's head. Oodako fled back to the beach and presumably returned to the sea, and Kong beated his chest and roared in victory.

Oodako also appeared in the title credits of Final Wars as the narrator talks about the numerous attacks on the world by the Kaiju. (Stock footage.)

War of the Gargantuas
In War of the Gargantuas, Oodako attacked a fishing boat, but was defeated by the Green Gargantua, Gaira.

Frankenstein Conquers the World
In an alternate ending for Frankenstein Conquers the World, after Frankenstein defeated Baragon, instead of being swallowed by the ground, Oodako came from the sea and fought Frankenstein. Frankenstein fought hard, but couldn't compete with Oodako's numerous and sticky tentacles. Oodako draged Frankenstein in to the water, seemingly to his death. After which, neither monster is seen again, in this movie.

Godzilla: Final Wars
Oodako was considered for Godzilla: Final Wars but for unknown reasons, he was dropped.

Trivia
Oodako is the only non-important monster to ever appear in three movies.