Dino Icthyo, also known as Theo, is a female Dino Knight whose creature form is the Ichthyosaurus. She possesses aquatic adaptations for superior mobility in water, including legs that fold into combat-efficient flippers. Her primary weapon, the Trident of the Tides, deploys attacks like "Bubble Blast" and "Flipper Storm" against adversaries.

Venerated by the ancient inhabitants of Atlantis as their fossilized protector, her background is defined by this connection. Reactivated in the present era, she joins the Dino Knights to defend Earth, emerging as the final knight discovered and activated during the conflict against the Dragozaurs.

Among her fellow knights, Dino Arch—who transforms into a shield—develops romantic feelings for her. The series leaves her potential reciprocation unclear and this storyline unresolved after their initial interactions.

Her documented appearances are within the television series episodes: "Welcome Back Theo," "Dino Icthyo in a Pinch," "Invasion of the Bite Lice," and "For the Earth."