The Mother was the enigmatic leader of Clan Mallacht.
Several thousand years prior to the events of The Daedra Wars, she was born. Not much later, she gained access to powerful magic and achieved immortality. The Mother would eventually develop a philosophy of enlightenment, similar to the Altmeri philosophy, that to achieve her true potential she had to transcend the limits of her body and reach the next plane of existence.
Clan Mallacht was brought into being, centered around this purpose. The clan was composed of disenfranchised and orphaned Bosmer, who the Mother brainwashed into being utterly devoted to her. Centuries prior still to The Daedra Wars, before she discovered Jephre's Spine, the Mother experimented with devising new ways to achieve immortality. One of these was transferring a mortal soul into an immortal body of her own making. Of these experiments, Scaldor was the most successful end result, as most of her creations either died or went insane. Scaldor eventually grew to hate her and killed her, but the Mother, being immortal, simply reconstituted herself. Scaldor would believe he had succeeded in killing her for centuries.
Her interest in Jephre's Spine would bring her into contact with the Covenant, who reluctantly aligned with her to retrieve the Horn of Stendarr. Eventually, they decided to try and apprehend the Mother for her crimes against humanity, of which included cannibalism and child sacrifice. She proved too powerful for them, however, and the Covenant had to blow the Horn of Stendarr, summoning Morihaus to battle her.
The Covenant escaped the Spine, which collapsed on top of the Mother and a mortally wounded Scaldor.
The Mother was a enigmatic, charismatic leader, able to successfully manipulate her followers as well as most she came across. Anyone who she couldn't charm, she could threaten with force, as she herself was a powerful sorceress with a large force of devoted warriors.
Although not malicious, the Mother was morally bankrupt, going as far as to needlessly force her followers to commit cannibalism, or murdering children for use in her magical experiments. She had a nurturing and warm side, one that was reserved entirely for people that she considered useful or of interest.
In terms of raw power, the Mother was a several thousand year old sorcerer who could completely recover from being set on fire or cut in half by a gigantic sword. A person struck by a single one of her spells would have been killed on impact. The only exception to this was Scaldor, who was still mortally wounded by it.