- Name: Iwao (イワオ)
- Classification: Kaijū
- Homeland: Planet Dokuro
- Age: 21
- Height: 166 cm
- Weight: 214 kg
- Chojin Kyodo: 150,000 Power
- Favorite Technique: Rocky Attack (岩石攻撃 Ganseki Kogeki)
- First Appearance: Manga Chapter 11, Anime Episode 4
Iwao (イワオ) is a rock Kaijuu who first appears at an amusement park and is subsequently defeated by Kinnikuman. He returns when Kinnikuman is being interviewed by Natsuko and plans to beat him up in front of her and ruin his image. His first attempt is interrupted by Kappatron so he tries to take Natsuko hostage, but he is still easily defeated by Kinnikuman. He then takes on the role of Kinkotsuman's sidekick and helps him with all of his attempts to destroy Kinnikuman. They seemingly turn good after the Choujin Olympics, but return as villains during the American Tag Tournament. In the anime, the two of them eventually join up with Detective Gobugari and act as Kinnikuman's main cheering squad.
Iwao is not that bright and frequently copies Kinkotsuman's laugh and speech pattern. For example, he frequently says dawasa (だわさ) (which Kinkotsuman often ends his sentences with) as a single sentence, seemingly meaning "I agree". This annoys Kinkotsuman and often prompts him to bop Iwao on the head. Iwao also refers to Kinkotsuman as Sensei.
- 1,000,000 Yen Quiz Winner (Tag?)
- Kinkotsuman's Underling
- Rock Kaijū (岩石怪獣, Ganseki Kaijuu)
- Single Cell (単細胞, Tansaibou)
- Thick Voice Iwao (ダミ声のイワオ, Damigoe no Iwao)