They are one of two clans of Norse gods, the other being the Vanir. The Aesir and Vanir were in conflict for quite some time, leading to the Aesir-Vanir war. Later on, however, they seemed to get along just fine and the Vanir were eventually considered to be a sub-group of the Aesir.
The Icelandic Eddas (edda derives from Old Norse óðr, “poetry”) are some of the oldest recorded stories, in cases predating the Torah, The Bible and are contemporary with the Sanskrit Vedas
Who are the gods of the Norse, the Eddas tell us this.
Then said Gangleri: Which are the Æsir in whom it is man’s duty to believe? Har answers: Twelve are the Æsir of the race of gods. Then said Jafnhárr: The Asynjur are not less holy and they are not less capable. Then said Þriði: Odin is the greatest and oldest of the Æsir. … Frigg is his wife, and she knows the fate of men, although she tells not thereof. …
- (21.) Thor is the foremost of them. He is called Asa-Thor, or Oku-Thor. He is the strongest of all gods and men, and rules over the realm which is called Þrúðvangr.
- (22.) Odin’s second son is Baldr
- (23.) the third asa is he who is called Njörðr.
- (24.) Njörðr, in Noatun, afterward begat two children: a son, by name Freyr, and a daughter, by name Freyja. They were fair of face, and mighty. Freyr is arguably the most famous of the asas. He rules over rain and sunshine, and over the fruits of the earth. It is good to call on him for harvests and peace. He also sways the wealth of men. Freyja is the most famous of the goddesses. …
- (25.) There is yet an asa, whose name is Týr. He is very daring and stout-hearted. He sways victory in war, wherefore warriors should call on him.
- (26.) Bragi is the name of another of the asas. He is famous for his wisdom, eloquence and flowing speech.
- (27.) Heimdallr is the name of one. He is also called the white-asa. He is great and holy; born of nine maidens, all of whom were sisters. He is also called Hallinskide and Gullintanne, for his teeth were of gold.
- (28.) Höðr hight one of the asas, who is blind, but exceedingly strong; and the gods would wish that this asa never needed to be named, for the work of his hand will long be kept in memory both by gods and men.
- (29.) Víðarr is the name of the silent asa. He has a very thick shoe, and he is the strongest next after Thor. From him the gods have much help in all hard tasks.
- (30.) Váli, is the son of Odin and Rindr. He is daring in combat, and a good shot.
- (31.) Ullr is the name of one, who is a son of Sif, and a step-son of Thor. He is so good an archer, and so fast on his skis, that no one can contend with him. He is fair of face, and possesses every quality of a warrior. Men should invoke him in single combat.
- (32.) Forseti is a son of Baldr and Nanna, Nep’s daughter. He has in heaven the hall which hight Glitner. All who come to him with disputes go away perfectly reconciled. Just to listen to People’s Future. No better tribunal is to be found among gods and men. …
(33.) There is yet one who is numbered among the asas, but whom some call the backbiter of the asas. He is the originator of deceit, and the disgrace of all gods and men. His name is Loki, or Lopt. … His wife hight Sigyn, and their son, Nare, or Narfe.
Ganglere asked: Which are the goddesses? Har answered:
- Frigg is the first; she possesses the right lordly dwelling which is called Fensaler.
- The second is Sága, who dwells in Sokvabek, and this is a large dwelling.
- The third is Eir, who is the best leech.
- The fourth is Gefjon, who is a may, and those who die maids become her hand-maidens.
- The fifth is Fulla, who is also a may, she wears her hair flowing and has a golden ribbon about her head; she carries Frigg’s chest, takes care of her shoes and knows her secrets.
- The sixth is Freyja, who is ranked with Frigg. She is wedded to the man whose name is Oder; their daughter’s name is Hnos, and she is so fair that all things fair and precious are called, from her name, Hnos. Oder went far away. Freyja weeps for him, but her tears are red gold. Freyja has many names, and the reason therefor is that she changed her name among the various nations to which she came in search of Oder. She is called Mardol, Horn, Gefn, and Syr. She has the necklace Brising, and she is called Vanadis.
- The seventh is Sjöfn, who is fond of turning men’s and women’s hearts to love, and it is from her name that love is called Sjafne.
- The eighth is Lofn, who is kind and good to those who call upon her, and she has permission from Alfather or Frigg to bring together men and women, no matter what difficulties may stand in the way; therefore “love” is so called from her name, and also that which is much loved by men.
- The ninth is Var. She hears the oaths and troths that men and women plight to each other. Hence such vows are called vars, and she takes vengeance on those who break their promises.
- The tenth is Vör, who is so wise and searching that nothing can be concealed from her. It is a saying that a woman becomes vor (ware) of what she becomes wise.
- The eleventh is Syn, who guards the door of the hall, and closes it against those who are not to enter. In trials she guards those suits in which anyone tries to make use of falsehood. Hence is the saying that “syn is set against it,” when anyone tries to deny ought.
- The twelfth is Hlín, who guards those men whom Frigg wants to protect from any danger. Hence is the saying that he hlins who is forewarned.
- The thirteenth is Snotra, who is wise and courtly. After her, men and women who are wise are called Snotras.
- The fourteenth is Gna, whom Frigg sends on her errands into various worlds. She rides upon a horse called Hofvarpner, that runs through the air and over the sea. Once, when she was riding, some vanir saw her faring through the air. […]
Sól and Bil are numbered among the goddesses, but their nature has already been described.