Mishann

Three years ago, a group of horde soldiers were sent to Northrend. Their mission was establish a base, cartograph the area and connect with the locals.

(...)

A few days after they set the camp, they were found by a scourge army, lead by Rivendare himself. This tragic encounter lead to the defeat of most of the troops and an even worse fate for the rest of them.

They were taken to Naxxramas and reborn as Death Knights, following the will of the Lich King. With new toys, Razuvious made the survivors fight in a small tournament to the death. Mishann was the last one standing.

When the Lich King invaded New Avalon and Havenshire, Mishann played a key role in the events that lead to the victory of that battle. However in the Battle for Light's Hope Chapel, Fordring was able to make the Lich King retreat to Northrend to avoid battle with the weilder of the Ashbringer on holy ground. After this, many Death Knights broke free from the Lich King's control.

Now she pledged her loyalty to the Dark Lady, as her goals are the same. Revenge for the cursed life she has...

She joined the Ice Age, a military group where she is Advisor. With the Ice Age, she went back to Northrend, and razed the cursed necropolis Naxxramas bringing an end to Kel'thuzad, the leader of the Cult of the Damned, who served the Lich King.