Mystra

Mystra, the Mother of all Magic, was a greater deity and the second incarnation of the goddess of magic, having been killed during the Time of Troubles. At the conclusion of the Godswar, Ao offered the position of Goddess of Magic to the cleric Midfire, who accepted and took on Mystra's name.

As a Mortal
Midfire was from a minor noble family in Halruaa, though there are no records of her real name. She was a woman of dark brown skin, dark blue eyes that resembled the color of deep water, and long, heavily curled natural hair. History regards her with the kindest eye, thinking her a gentle, caring woman, with an insatiable desire for learning that caught the original Mystra's eye, making her a priestess.

Popular belief is that Mystra personally watched over her during her life. Dissident beliefs are that she formed pacts with devils, fey, or was the consort of various gods, and managed to gain favor in the heavens that way. However, there is no doubt that she trained and studied tirelessly, her writings survive in most of Faerûn's popular colleges.

Ascension
Midfire's position was granted to her by Ao, who deemed her most fit to fill in the gap left by Mystra.

Death
She was stabbed twice in the chest by Cyric. The origins and properties of the two weapons remain unknown, but it's certain that he had her cut off from the Weave first. It seemed to be her willing decision to block her connection from the Weave.

Relationships
Kelemvor was her lover, but there's arguments as to whether or not she was closer to Adon or Cyric in her time traveling together. As they began to feud, she seemed very conflicted, and referred to one of them as her "greatest and dearest ally", though there's no specific implication as to who that was.