The Æsir (Old Norse: singular "ǫ́ss" or "áss"; feminine "ásynja", plural "ásynjur") are the principal group or tribe of deities in Norse mythology. Including Odin, Frigg, Thor, and Baldr, the Æsir reside in the realm of Asgard, situated at the top of Yggdrasil's highest branch. Alongside the Æsir exists a second family of gods known as the Vanir, who joined with the Æsir to form a single, unified pantheon after the devastating war between the two tribes of deities. The Vanir were native to Vanaheimr, the god Njörðr and his children, Freyr and Freyja chief among them. The Æsir gods were usually connected with power and war, while the Vanir were associated with fertility and nature.