The first Harvester was created by the smiths of Amgarrak Thaig, who were attempting to replicate and improve upon on Caridin's work on creating golems. The smiths used the corpses of castelessdwarves instead of metal and stone, claiming that "It would be an honor for a casteless dwarf to die in such way". Nereda, the Tevintermage with the expedition in Amgarrak, used blood magic to seal a Fadespirit inside the construct made of flesh and bone. When the construct came alive, the head removed itself from the body and disappeared, becoming the first Harvester. It killed numerous people in the thaig and after witnessing what their twisted creation was capable of, they were forced to trap it in a level of the Fade via the use of the Lyrium wells and seal the thaig. Since then, people have long forgotten about both the Harvesters and the thaig.
Harvesters set about gathering the flesh of the dead to add to their bodies to create a sort of flesh golem which they use like an armor. It seems that the Harvester is capable of manipulating the Lyrium wells and using them to its advantage.
It's also seen that, with a secret ritual of blood magic, a living mage can willingly merge with a large number of corpses and become a Harvester.
This section contains spoilers for: Golems of Amgarrak.
A Harvester attacked the Warden-Commander as well as Jerric and Brogan of House Dace in Amgarrak. After discovering the truth behind the Harvester's origins, the trio resolve to destroy the creature and bury this branch of golem research forever. They finally succeed in cornering the Harvester at the Thaig's forge. The battle is pitched and the Harvester shifts the party through different levels in order to become more powerful and unleashes waves of animated corpses to attack them. After a fierce battle the Harvester is finally slain. However the structural damage caused during the battle causes Amgarrak to begin to collapse. Although the Warden-Commander, along with Jerrik and Brogan Dace, escape the crumbling thaig, it is discovered that was not the only Harvester and waves of other Harvesters flee out into the Deep Roads.
This section contains spoilers for: Dragon Age II.
First EnchanterOrsino, driven to suicide at the sight of the Right of Annulment, turns into an improvised Harvester in the midst of the battle, performing a ritual of blood magic he learned from the research of Quentin to merge with the corpses of Circle mages. After killing several Templars, the Harvester turns on Hawke and their companions. Eventually the Champion of Kirkwall managed to rip its head off before stomping the creature to death.