In Norse mythology, the meaning of the name Aegir is associated with water. He was also called Hler and Gymir [the Blinder] (the name of Gerd's father -- it is not known if they are one and the same). Aegir was the god of the seashore or ocean, and called the ruler of the sea by Snorri. He was a personification of the ocean, be it good or evil.
He caused storms with his anger and the skalds said a ship went into "Aegir's wide jaws" when it wrecked. Sailors feared Aegir, and thought he would sometimes surface to destroy ships. According to Sidonius, early Saxons made human sacrifices to a god of the sea, possibly connected with Aegir.
Aegir was one of the Vanir and a giant. His father was Mistarblindi [Mist-Blind], and his brothers, Logi [Fire] (identified by Guerber as Loki), and Kari [Air]. Aegir's wife (and sister) was Ran and they lived under the sea by the island Hlesey. Ran and Aegir had nine daughters who were the waves -- all of their names are poetic names for waves.
Aegir brewed ale for the gods after Thor brought him a big enough kettle. Every winter the gods would drink beer at Aegir's home. He was, therefore, famed for his hospitality. Instead of having a fire, gold was put onto the floor of the hall to provide light. Gold is therefore called Aegir's fire. The cups in Aegir's hall were always full, magically refilling themselves. Aegir had two servants in his hall, Fimafeng [Handy] and Eldir [Fire-Kindler]. According to Lee Hollander, Aegir's function as the gods' ale brewer was suggested by the ocean's foam.
After the death of Balder, the gods gathered for a feast in Aegir's hall. Loki showed up and insulted everyone (this is told in Lokasenna in the Poetic Edda). The gods couldn't do Loki harm in the hall since it was a sanctuary where no violence could be committed.
It is interesting to note that in Snorri's Gylfaginning [see Edda] Aegir is not mentioned as one of the gods, and in part of his Skaldskaparmal Aegir, also referred to as Hler, was a man "very skilled in magic" living on the island Hlesey who went to visit the gods in Asgard. During his visit he listened as Bragi told him of the gods' adventures.
In Egil's Saga, after the death by drowning of Egil's second son Bothvar, Egil composed the poem Sonatorrek which mentions Aegir:
Sure, if sword could venge
Such cruel wrong,
Evil times would wait
That wind-giant's brother
Were I strong to slay,
'Gainst him and his sea-brood
Battling would I go.
But I in no wise
Boast, as I ween
Strength that may strive
With the stout ships' bane.
(Leach, A Pageant of Old Scandinavia, p. 321.)
(Nicole Cherry, A list of Norse Beings, http://www.ugcs.caltech.edu/~cherryne)