Gravers are undead human slaves controlled by the Tall Man and they appeared in all the Phantasm movie series.
The seemingly stronger type of Gravers are Demon Troopers.
These zombies were created from cadavers of recently killed people by the Tall Man through a secret process almost similar to that of the Zombie Dwarves. They too kidnap or kill people and spirited off their dead bodies to a hoary and dark dimension where the Tall Man awaits and adds them to his legion of the living dead.
The Gravers were no more when the same young man who escaped the Tall Man, discovered the secret of the undertaker's origin and found a way to his unhloy reign of terror.