Released on October 11, 2011, Mark Of The Assassin adds a new party member to the game: Tallis, an Elven Assassin voiced and modeled after actress Felicia Day, and also the lead character of the Dragon Age: Redemption webseries. In the DLC's featured quest, Hawke must help Tallis infiltrate an Orlesian estate outside Kirkwall and steal a precious relic.
Source: Wikipedia, "Dragon Age II", available under the CC-BY-SA License.