Seth, or Set, was regarded as the Lord of Lower (Northern) Egypt and was represented by a big-eared imaginary animal resembling a donkey or maybe an aardvark. He was associated with the desert and storms. The Greeks associated Seth with their god, Typhon. When Upper Egypt conquered Lower Egypt, Seth became known as the evil enemy of Horus (deity of Upper Egypt). Seth was the brother of Osiris, Isis as well as Nephthys who was also his wife. Some legends also name him as the father of Anubis. During his battles with Horus, the goddess Neith suggested a compromise by giving Horus the throne, and Seth the Semetic goddesses Astarte and Asat. Seth is most famous for the fratricide of his brother Osiris and the attempted murder of his brother's son, Horus. Horus survived though and avenged his father's death by ruling all of Egypt and exiling Seth to the desert for all time. Seth was not completely evil though, he protected the sun barge of Re during its nightly journey through the underworld and he fights the snake-like monster Apep. Also, for a short time during the 19th Dynasty respect grew for Seth as he was seen as a god who restrained the forces of the desert.
Text taken from http://www.angelfire.com/hi/saosis/right.html.