Apophis
Apophis has been the most frequently encountered Goa�uld.  He was seen capturing Skaara and his sister Sha�re and used them both as hosts.  He is called the serpent God which blends in nicely with the Mythology of Apophis.  Teal�c was his First Prime until he betrayed him and helped the humans.  He has two children. The Harcissus, with Amaunet and, Klorel, with Hathor.  Apophis �gave life� to Klorel, therefore Klorel calls Apophis his father.  He was also the first Goa�uld in Stargate the series and made his first appearance in �Children Of The Gods�.  His other appearances were in The Nox, Cor-Ai, Within the Serpent's Grasp, Serpent's Lair, Family, Secrets, Serpent's Song, Point of View, Rules of Engagement, Jolinar's Memories and The Devil You Know.  In the episode, "Serpent's Song" Apophis died at the SGC base and returned his body to Sokhar to prevent an attack on Earth.  According to Martouf, a Tok�ra, Sokhar would torture Apophis endlessly with the help of the Sarcophagus

Peter Williams is the actor of Apophis and he does his job brilliantly! 

Mythology of Apophis
Apep was a Epgyptian monster that lived in "perpetual darkness�.  This snake God is the chief of antagonists from the sun God called Ra.  Every night, Apep tries to stop Ra going through the Underworld.   Apep is the symbol of darkness, evil, and chaos.  The Greeks called and referred him as Apophis.

Check here for more details
http://www.pantheon.org/mythica/articles/a/apep.html

Pictures of Apophis