John doesn’t sleep and keeps fighting

“He's a Dog of War, known in some circles as Dog Tags. I think his name is an older equivalent to John Doe, but for soldiers. When warzones are at their ugliest and most chaotic, and people start losing track of who is where, who is alive and who is dead, certain Others may crop up on the battlefields. Ones that fight, so long as there is conflict around them. If the soldiers in that war are killing innocents, so will the Dogs of War. If they commit other atrocities, so will the Dogs. They don't sleep, they keep the battle going, and as long as the battle continues, they don't stay down. Related to Revenants, but Revenants are the province of Death, not War."

- Lost for Words 1.4