Mystra

She is the Mistress of Magic and Mother of Mysteries who guides the weave of magic that envelopes Toril. She tends to the weave constantly, making possible all the miracles and mysteries wrought by magic and users of magic. She is believed to be the embodiment of the Weave and of magic herself, her veins the ley-lines, her breath the mists and her body the pulsing, thrumming earth.

She is a Neutral Good (previously, and still also, Lawful Neutral) Greater Power. Her symbol is a ring of seven stars surrounding a rising red mist, spiralling to the heavens, though her older and often seen symbol is a simple seven-pointed star. Her divine realm is Dweomerheart, and her Third Edition D&D domains are Good, Illusion, Knowledge, Magic, Rune, and Spell.

Dogma
''Love magic for itself. Do not treat it just as a weapon to reshape the world to your will. True wisdom is knowing when not to use magic. Strive to use magic less as your powers develop, for often the threat or promise of its use outstrips its actual performance. Magic is Art, the Gift of the Lady, and those who wield it are privileged in the extreme. Conduct yourself humbly, not proudly, while being mindful of this. Use the Art deftly and efficiently, not carelessly and recklessly. Seek always to learn and create new magic.''

Orders
The Starry Quill is an order of Mystran bards who often work as information gatherers and rumormongers for the church or spend part of their time in designated libraries unearthing magical knowledge and then preserving it for posterity.
 * Order of the Starry Quill

The Church of Mystra sponsors an order of rangers, known as the Order of the Shooting Star. These rangers receive their spells from Mystra. They serve as long-range scouts and spies for the church and also deal with magical threats that threaten the natural order of things, such as unloosed tanar'ri and baatezu and creatures born of irresponsible wizardly experimentation.
 * Order of the Shooting Star

The Church of Mystra sponsors a knightly order of paladins, the Knights of the Mystic Fire, who are granted their spells by Mystra. They often accompany members of the clergy on quests to locate lost hoards of ancient magic and also form the cadre from which the leadership for the small groups of armed forces who guard Mystra's larger temples and workshops is drawn.
 * Knights of Mystic Fire

Aside from just being a Greater Power, Mystra has a secret revealed in "Shadows of the Avatar," Elminster's personal quest during the Time Of Troubles Series. It states she is more powerful than any god (save Ao) but therein lies the secret. Roughly half of her power lies in her Chosen and in the Lesser Power Azuth, thus planned by Ao so Mystra does not rule all Realmspace.

Incarnations
Originally called Mystryl, Mystra came into being after the previous incarnation sacrificed herself to save Faerûn from the destruction Karsus of Netheril nearly brought upon them. During the Time of Troubles, Mystra was killed by the deity Helm for defying the god and trying to climb the Celestial Stairway to the heavens.

Her death caused great damage to the Weave, but the young mortal Midnight was chosen to succeed the goddess as the next Mystra -- eventually restoring the magic of Toril. Midnight killed Myrkul in a duel in the skies over the city of Waterdeep.

Relationships
Mystra's greatest enemies are Shar, who created the Shadow Weave to oppose Mystra's Weave, and Cyric, who was a mortal along with Mystra and Kelemvor (with whom Mystra has a cold friendship). She is served directly by the Lesser Power Azuth, and indirectly by demipowers Savras and Velsharoon. Mystra also has powerful mortal servants in her "Chosen" - including Elminster, Khelben Arunsun and the Seven Sisters.