|Home world:||Planet Earth (Tiga's universe)|
|First appearance:||Ultraman Tiga Episode 43: "Land Shark"|
|Affiliation:||Keigo Masaki (Master)|
Evil Tiga (in-game)
Subtitle: Underground Shark (地中鮫 Chichū Same?)
- Length: 48 m
- Weight: 53,000 t
- Origin: Kumamoto Prefecture Underground
Geozark was the byproduct of the mad scientist Keigo Masaki for him to know who the real identity of Ultraman Tiga is. Geozark first appeared nearby Kumamoto and was about to attack its castle until GUTS arrived and tried to track it. Geozark then disappeared underground before GUTS could do anything else. Later Geozark appeared again, heading towards Mitsui Green Land Amusement Park, threatening to kill several people and children around the park. Goaded by Masaki's advice, Daigo transformed into Ultraman Tiga and managed to pull Geozark out of the ground before it could endanger anyone. After Tiga went into Power Type, he was able to overpower Geozark in battle, but not without Geozark hitting Tiga with a powerful blast of its laser (thanks to the help of its master provoking Tiga.) Despite his recent injury, Tiga was able to destroy Geozark with his Delacium Light Stream, but Geozark's deed was done and Keigo had what he needed.
- Suit actor: Toshio Miyake.
- Geozark's roar is a reused Gagi roar.
- Geozark is the only Kaiju in Ultraman Tiga, intentionally created by humans.
- Geozark is seen on Ultraman Fighting Evolution 3 as support character for Evil Tiga but not playable.
- Due to the drill nose and aquatic appearance, Geozark may have been inspired by the monster Gubila.
- Although not appearing in the movie, Geozark (Along with Gobnu Oguma, Kyrieloid & Bizaamo) appears in Daigo's flashback in Ultraman Tiga: The Final Odyssey.
Powers and Weapons
- Burrowing: Thanks to the drill-like feature of his nose, Geozark can burrow at high speeds.
- Energy Beam: Geozark can fire a light blue beam of energy from its nose.
- Extraordinary Jumper: Geozark can jump far distances.
- Geozark Attack (ゲオザークアタック Geozāku Atakku?): Evil Tiga rides on top of Geozark's fin, sliding towards the opponent before he delivers a kick attack. This cannot be considered as a tag-team attack, as Geozark's role is only a supporter and is a part of Evil Tiga (player)'s attack.