Moby Deep is a character that appears in Sonic Underground. He is a giant whale who roams the oceans of Mobius.
During his life, Moby Deep is mistaken for a sea monster, who is sinking many ships on the ocean of Mobius. This makes people scared and turn to Doctor Robotnik's side in order to receive protection from the sea monster. However, it later turns out to be one of Robotnik's schemes. Moby Deep is first seen saving Sonic the Hedgehog from drowning. Moby told him he is afraid of submarines, because they able to hurt him. He then helps Sonic back to the ship. Later on, Moby Deep is seen again chasing Sleet and Dingo as intending to eat them for dinner.
- Moby Deep is a prominent parody of Moby Dick, who apparently is voiced by the late Long John Baldry who also previously voiced Dr. Robotnik in Adventures of Sonic the Hedgehog.