Corypheus

Corypheus also known as The Elder One is the main antagonist of DLC ''Dragon Age 2: Legacy and a game Dragon Age: Inquisition. He's a'' mysterious entity served by the Venatori as the Elder One. He is relentless, ambitious and beyond arrogant as he believes he operates on a level no other being can comprehend.

History
Corypheus is a Tevinter magister who heeded the call of the Old God Dumat and the time during which the Free Marches belonged to the Imperium has long since passed.

Some time after the First Blight, the Grey Warden Sashamiri imprisoned Corypheus in a tower stemming from the Deep Roads in the middle of the Vimmark Mountains. Interrogation proved futile, as any Warden in his vicinity became mysteriously drawn to his influence. When removed from the area, they would have forgotten anything prior, and would be left dazed.

Interestingly, it appears that Corypheus emits a type of Calling to anyone bearing the Taint, similar to the Old Gods, which draws darkspawn and Warden alike to his prison.

Malcolm Hawke was responsible for restoring the seals on Corypheus' prison using blood magic, which the Wardens use from untainted mages since before the founding of the Chantry.

Dragon Age II
Corypheus is involved in the Legacy quest. The Grey Warden Janeka wants to utilize him as a weapon to combat the Blight, while the former Warden-Commander of the prison, Larius, wishes to kill him before he escapes the prison due to the weakening seals. Eventually Corypheus is released and speaks briefly to Hawke and their companions before attacking them in confusion.

As Hawke delivers Corypheus the final blow, Corypheus will look at Larius or Janeka and faintly smile. Then as Corypheus is struck down, Larius or Janeka can be seen shuddering in the background before stumbling. Corypheus' eyes will also glow upon seeing Janeka or Larius.

Regardless of who Hawke sides with, Janeka or Larius will ominously thank Hawke for their assistance in a very different tone of voice from before and leave. It is possible that Corypheus, though defeated, has possessed the body of the surviving Warden to escape his prison, similar to how the Archdemons can possess bodies of the nearest Darkspawn, should a non-Warden strike a fatal blow to them. Additionally, Cassandra will question Varric's story as she says the Wardens she met at the ruins of the prison told her nothing of Janeka/Larius, which suggests the surviving Warden never returned to the Order. When asked if there is anything else to his tale, Varric replies that there is, but that it hasn't happened yet.