The Aesir and Vanir are the two sects of gods in Norse Mythology. The Aesir are the gods and goddesses of war who live in Asgard, and the Vanir are the fertility gods who live in Vanaheim. Eventually these two groups of deities entered a war against the other, and after much strife, the Aesir won out.
The Major Aesir Gods:
Odin- the chief god in Norse Mythology...in fact, one of his alternative names literally means "Allfather." He is the god of war, death, poetry, and wisdom. Carries the spear named Gungnir and on his shoulders sit the ravens Huginn (Thought) and Muninn (Memory). Is known as a seer, and has only one eye.
Thor- son of Odin. God of thunder. Bringer of justice and order, carries the hammer Mjollnir.
Hel- goddess of the underworld, Helheim. Daughter of Loki, beautiful woman from about the shoulders up, decaying/rotting flesh below...the legend of Annis is sometimes thought to be contrived out of this goddess.
Loki- the son of giants, trickster god, father to three monster children: the wolf Fenrir, the half alive/half dead Hel, and the serpent Jormungand. He leads the giants and monsters into battle against the gods and heroes.
The Major Vanir Gods:
Freyr and Freyja- twin brother and sisters. god/goddess of fertility. The most noble duet in the pantheon of Norse Gods. Freya= love and war, Freryr= god of plenty.
Njord- governed the sea and the winds and guarded ships and seafarers. Married to the frost giantess Skadi, father to Freyr and Freyja and the frost giant Gerd.
Nanna- the moon goddess, Balder's loyal wife whose heart broke at the sight of him lying dead that she was cremated with him and accompanied him to Hel.