Dumat

Dumat, the Dragon of Silence, was the first and the most powerful among the Old Gods, ancient draconic beings said to be imprisoned underground by the Maker for usurping His worshipers.

Dumat was the first of the Old Gods to be tainted by Darkspawn influence, which brought about the First Blight.

Background
Dumat is believed to have originally taught blood magic to Archon Thalsian, the founder of the Tevinter Imperium.

The early human kingdom of Barindur is said to have completely vanished in -1610 Ancient after losing favor with Dumat. Only a path and bare rock remain.

After the fall of the magisters in -395 Ancient (800 TE), the first darkspawn burrowed into Dumat's underground prison, where the Old God was corrupted and transformed into the first archdemon, launching the First Blight. Dumat was finally slain by Grey Wardens at the Battle of Silent Fields in -203 Ancient (992 TE), after almost 200 years and approximately 1,000 years before the events of Dragon Age: Origins.

While the Chantry insists the darkspawn created the first Archdemon, some ancient lore says that Dumat created the first darkspawn and led them against Thedas.

Culture
There was a holiday dedicated to Dumat back in the times when the Old Gods were still widely revered. It was called "Funalis" but this holiday is now known as All Soul's Day and is spent in somber remembrance of the dead. It is celebrated at the beginning of Matrinalis.

Trivia

 * The name may be a reference to Dumah, the "angel of silence" in Jewish Religion.
 * In Dragon Age: Origins - Awakening, the player can acquire weapons rumored to have been made from Dumat's bones: the sword Dumat's Spine and the dagger Dumat's Claw.