|Home world:||Planet Earth (Nebula M78 Universe)|
|First appearance:||Ultraseven episode 42: "Envoy of Nonmalt" (1968)|
Subtitle: Octopus Monster (蛸怪獣 Tako Kaijū)
- Height: 30 m
- Weight: 10,000 t
- Origin: Pacific Ocean seabed
One day, two large ships blew up and were set aflame. After the Ultra Garrison tried to find an eyewitness that saw what happened, their luck ran short. However, some time later, the monster Guyros made himself known as he started attacking another large ship. The Ultra Garrison arrived on the scene quickly and managed to kill Guyros by attacking him from the air and water. Little did anyone suspect that Guyros was only a pawn in the Nonmalt's plan. Guyros was revived by the Alien Nonmmalt later that day after they started to attack a local harbor town with a very powerful submarine. Dan Moroboshi turned into Ultraseven and intercepted Guyros, but the creature proved to be a formidable adversary until the hero used the environment against him. Ultraseven used his Eye Slugger to slice off each of Guyros' tentacles after each dive, slowly making him incapable of fighting. Shortly into battle, Guyros became tired out and simply died.
- In the middle-to-late 1990s, footage of Guyros was used for the TNT, TBS and Cartoon Network show Cartoon Planet. Guyros footage was used to depict an alien in the recurring sketch entitled 'Messages from Outer Space' that would feature other Ultraseven Kaiju broadcasting to Space Ghost, Zorak and Brak on Cartoon Planet. In his featured message, he was called Barnacle Boy (with no relation to the Spongebob Squarepants character), broadcasting from Denada 7 the Underwater City. He reappeared in another recurring sketch called 'Vacation Spots of the Universe', concerning a location advertised as Mr. Beak's Underwater Thrill Park.
- Guyros has a reused Gyaos roar.
- Guyros' roar would later be used on the Ultraman Jack kaiju Arstron.
- Guyros' design is based off of the silver prize winner of a kaiju drawing contest, Alien Guyros (ガイロス星人 Gairosu Seijin). The suction cups were one of the features carried over.
- In the TNT dub, Guyros is referred to as a robot.
Powers and Weapons
- Adept Swimmer: Guyros can swim at medium speeds.
- Tentacles: Guyros has six tentacled arms used for whipping and constricting foes.