Aegir was not a particularly well liked God.  He is credited in riding over the tops of the waves and capsizing ships and seizing their crews for amusement.  His wife-sister, Ran, was also a sea deity.  She oversaw men who perished at sea, but many of those men perished because she would pull them overboard. Needless to say, the Norse people very much disliked Ran.  This was most likely a very large factor in Aegir loosing dominance as the chief sea god. 

Aegir and Ran live in an underwater hall off the coast of the island of Hlesey.  They had nine daughters, the Wave Maidens who were beautiful giantesses. It was the Wave Maidens that Odin mated with and from that union came Heimdall (all nine Maidens were his mother as they gave birth simultaneously).

Aegir was known for his skill at brewing ale.  It was this skill that was the center of one Thor's adventures.  During one of the many feasts of the gods, there was a shortage of ale.  Tyr and Thor immediately left for the watery hall of Aegir.  Upon arrival, they demanded that Aegir brew more to end the shortage.  Not being terribly impressed with the demand, Thor was told that in order to brew enough, he would need to find a large cauldron.  Tyr volunteered the large cauldron belonging to his father, the giant Hymir.  After many challenges from Hymir, Thor was successful in winning the use of the cauldron.  Aegir then brewed a more than ample amount of ale to satisfy the gods.