Dr. Depth is a deep sea criminal. By his lastname, Depth it means the deapest part of the sea. Most he loves playing in the sea but he hates dry land or air. As seen he is the most wanted criminal underwater. But there aren't any criminal hidding undersea which leaves that he is only the first.
People can't see him because he is always underwater but he wears materials so he can live underwater as astronaut clothes (look-like) and big oxygen tanks.