Triton is an Inhuman.
When the Great Refuge was trapped, one of the few good things Maximus did was to create a special harness that allowed Triton to breathe air. Eventually Black Bolt used his voice to break the barrier and the Inhumans went to a new home.
Background
Triton was voiced by Rocky Carroll and Mark Hamill.
The first version of the character outside the comics and only animated version.