One of the more common epithets was that he was 'great of strength'. In one of the Pyramid Texts it states that the kings strength is that of Set. The Pharaoh himself was the heir to the two 'brothers' and united the offices of Horus and Set or of Upper and Lower Egypt.
Set protected the sun (Re) as he journeyed through the land of the dead during the night. Most notably, he fought and killed Apep, the evil serpent of darkness who attacked Re each night.
Later, when his brother Osiris became a much more important god, Set gradually became thought of as his opposite. A new myth cycle developed in which Set kills Osiris in their struggles (see Legend of Osiris and Isis), so he became the god of evil.
He was also seen to be in contrast to Horus, who was a god of the sky, so his breath was responsible for the worms. Metal ore was called the "bones of Set" because they came from the ground. In the 3rd millennium BC, Seth (replacing Horus) became the patron god of the pharaohs, but as the story of Set's murder of his brother became popular, Horus was switched back.
Set is sometimes incorrectly thought of as being a jackal-headed god. He is depicted as having square ears, a forked tail and a curved snout. Some people believe the animal represented was an aardvark, a type of pig, or another as-yet-unidentiifed beast. In addition to the already mentioned animals, Set was associated with gazelles, donkeys, crocodiles and hippopotami.
The Greeks later linked Set with Typhon because both were evil forces that attacked the main gods, though they are not otherwise very similar.
See also: Legend of Osiris and Isis; Temple of Set.
Alternative: Seth, Setekh, Setesh, Seti, Sutekh, Setech, Sutech