The pet of the royal family of the Inhumans. Lockjaw first appeared in Fantastic Four #45.

The Inhumans are a forced genetic offshoot of the human race created by the Kree, an alien race. They existed for many years upon the Earth without the knowledge of the general human populace. They are ruled by a king who is appointed due to his genetic superiority. Members of the royal family are exposed to substance that quickens genetic advancement. The substance called Terrigan mist causes the members of the royal family to have special powers and abilities. The current royal family has a pet dog called Lockjaw who has been exposed to this genetic catalyst. exposure caused the dog to have a number of special abilites.

First, Lockjaw is much larger than a normal dog, being about five feet tall at the shoulder. His larger size also give Lockjaw great strength, enabling him to dig through concrete with his paws. Exposure to the mist also gave him immense strength in his jaws enabling him to bite down on something and not let go. His strength is such as to keep the Thing from being able to remove his hand from Lockjaw's mouth.

Lockjaw also has the ability to teleport himself and others over vast distances and even across dimensions. Those teleported with Lockjaw must be in the area of him or touching him to be teleported. Lockjaw's teleportation ability seems linked to the forked antenna that comes out of his forehead.

Exposure to the Terrigan mist also enhanced Lockjaw's natural canine tracking ability allowing him to track people and things over vast distances and even across dimensions. As Lockjaw could not do this with his sense of smell, the mist made the ability psionically based rather than based on smell.

At one time, the mutant Quicksilver attempted to expose his daughter Luna to the Terrigan Mists to give her superhuman powers. The Thing attempted to stop him and eventually did so. During this adventure, Lockjaw seemingly spoke to the Thing telling him that he had once been human too, but exposure to the mist had given him this dog-like appearance. It was later revealed that the whole episode was an elaborate practical joke on Ben Grimm by members of the royal family, who used the antenna on Lockjaw's head as a tuner to allow them to broadcast the voice.