Marixx was a human female Warlock. During the Burning Legion's third invasion of Azeroth, Marixx interrupted a ritual of Gul'dan and stole the Scepter of Sargeras. However, she was later captured by demons and brought to the Twisting Nether, where Sargeras offered her a choice: serve the Legion willingly, or be forced to. Marixx reluctantly agreed to serve them.
With no intention to actually aid the Legion, Marixx helped push back against them in the Broken Isles, while making small efforts to help them so she would not be exposed. The Burning Legion, however, eventually caught on. When Marixx landed in Suramar with a party of Alliance soldiers, she was mind controlled and forced to kill them. Marixx was then forced to use their souls and the Scepter of Sargeras to open a portal to the Twisting Nether, allowing demon reinforcements into Suramar. Marixx was then freed of her mind control, captured by demons, and taken to Suramar City, where she was made a slave of the Legion who could relive her actions in horror and watch as her allies were defeated.
During the siege of the Nighthold, Marixx attempted to attack Legion forces and escape from Suramar City. However, Gul'dan forcefully took control of Marixx's mind. She was later freed from serving the Legion following Gul'dan's defeat.
Marixx soon reclaimed her place as Netherlord of the Black Harvest, and helped the Armies of Legionfall on the Broken Shore. She would later help put an end to the Legion on Argus.
World of Warcraft: Wrath of the Lich King
World of Warcraft: Warlords of Draenor
World of Warcraft: Legion