The Æsir are the principal gods of the Norse pantheon. They include many of the major figures, such as Odin, Frigga, Thor, Baldr and Tyr. A second clan of gods, the Vanir, is also mentioned in the Norse mythos: the god Njord and his children, Freyr and Freyja, are the most prominent Vanir gods who join the Æsir as hostages after a war between Æsir and Vanir. The Vanir appear to have mainly been connected with cultivation and fertility, the Æsir with power and war.
The interaction between the Æsir and the Vanir is an interesting the two clans of gods fought battles, concluded treaties, and exchanged hostages (Freyr and Freyja are mentioned as such hostages).
The Æsir stayed forever young by eating the apples of Iðunn, although they could be slain, as it was predicted that nearly all will die at Ragnarök.