She Who Must Not Be Named is a bane of tremendous power which lurks deep beneath Mount Thunder. At one time she was the cosmic embodyment of Love, just as Lord Foul is the cosmic embodyment of Despite, but was then betrayed by the Despiser and trapped within the Arch of Time. As a result of this betrayal, she was transmogrified into a being of pure rage, hatred, sorrow, and madness; a bane comparable to the Despiser himself.
In Against All Things Ending, she was awakened by the battle between Thomas Covenant, his son, and Linden Avery, in the Lost Deep. She was revealed to be a being composed of the lost souls of numerous women who had been betrayed; including Kastenessen's lost lover, Diassomer Mininderain (the Creator's former wife), and the Auriference. The Ardent, an Insequent chosen by his people to serve Linden Avery and to assure the success of the Harrow's purpose, tried to transport the company to safety, but the arrival of Esmer precluded the Ardent from assisting them in this way.
The sheer power of the bane drove Linden Avery into a catatonic state of pure horror and despair. Thomas Covenant attempted to reason with She Who Must Not Be Named by showing her his white gold wedding band as a reminder of who she used to be. This proved unsuccessful, and so he then demanded that Esmer reveal her true name; which might release her from her torment. However, Esmer refused to comply on the grounds that were her name to be returned to her, the result would be comparable to the breaking of the Arch of Time.
In a final attempt to keep her from killing them, Covenant enlists Anele to talk to the Dead in Andelain, who send the spectre of High Lord Elena to distract She Who Must Not Be Named, who relishes Elena's private despair. As Elena is being devoured by She Who Must Not Be Named, Covenant manages to convince Esmer to depart, thereby allowing the Ardent to transport the company to the safety of Landsdrop.