Death was a Hive queen, being young, barely out of her adolescence when she made herself known, inexperienced but having the drive and decisiveness in her decisions that made her an effecive leader enough that she formed her own alliance of Hives during the Wraith civil war.
With her claiming the Mantle of Coldamber, a Queen with the mind far more powerful of normal Queen and lineage of the First Mother Night, she was nearly unopposed in bringing the factions together until Atlantis returned to Pegasus. She is also responsible for reuniting the Wraith into a single group once again and, later on, is successful in kidnapping Dr. Meredith Rodney McKay to force him to get the Hive ship's hyperdrive working so that the Wraith can eventually get to Earth in the hope of conquering it.
Death not only forced McKay to create a more efficient hyperdrive system for the Hive ships but also converted him into a Wraith named Quicksilver who served her loyally and had him create effective shielding technology for at least a single Hive ship and Cruiser during a mission to probe Atlantis' defenses.
Both ships were destroyed in the ensuring battle between the Daedalus and the George Hammond but proved effective enough for the Wraith ships to damage the Hammond before destruction. She died during the battle.(SGA, "The Lost")