Shards of the Shattered Pact: Seowyn's Crossing
Ythmaurg Verenthalak was a Dragonborn who fought with Gryphon Company under Dame Kebesh Aurumadrath during the War of the God King. At the Battle of Kebeshkrak’s Stone, he fought by her side for several weeks. It is believed, however, that he was approached by orcish spies who offered him riches to betray his commander. Other rumors state that he fell to the worship of Tiamat out of desperation not to die and that she directed him to betray Dame Kebesh.
Whatever his true motives, it is known that, after three weeks of the battle, He stabbed Dame Kebesh in the side with a poisoned dagger. Although she wasn’t killed by this, she was weakened enough that the Orcish Hordes were able to overrun and kill her.
Ythmaurg fled into obscurity after the battle, as his fellow dragonborn were desperate to find him and bring him to justice. While his ultimate fate is unknown, it’s generally assumed that he died under an assumed name, fading into legend only as a betrayer.