The Aesir gods are the gods that descend from Odin and that make their home in Asgard.
They were the crude counterparts of the Vanir, being the gods of war, death, power, and destruction. They were the lords and ladies of the sky. Famous Aesir include Thor (the god of thunder, strength, and holiness) and Baldr (the god of beauty, sunlight, and summer).
The Aesir were not immortal (they could be killed in battle), but they were forever young. They owed this to the apples of immortality, which were provided by the goddess Idunn.