The Sustem Lords
Anubis
In Stargate
A Goa'uld whose crimes were so bad that even the Goa'uld despised him and exiled him. Thought to have died a thousand years ago he has just returned. His technology outmatches that of the other Goa'uld and rivals the Tollan. He has defeated an Asgard warship and has downloaded Thor's knowledge into his computer, however he has lost the ship the computer is on as Thor managed to take control of the ship and take it to Earth. He has recently taken a lot of new minions, including the once powerful Osiris and 2 of Apophis's personal minions Zipcana (affectionately known as Zippy) and Tanith, although the latter has now died. He has attacked and severely weakened many of the System Lords with ease as well as wiping out the Tollan and crippling the Tok'Ra, yet his territory is still greatly lacking. He does seem to be trying to expand it as Tanith was scouting a planet for a new base in "48 hours". Osiris met with the System Lords in "Summit" where she initiated a vote to allow Anubis back from his banishment to rejoin the ranks of the System Lords. All but Yu voted for him to join them, but before he did he would wipe out the Tau'ri as he was not yet a System Lord, a small flaw in the Asgard's Treaty. He tried using a meteor made of Naquadah to trick the Tau'ri into launching a missile and wiping themselves out, whilst preventing Asgard intervention as it was a natural disaster. After his failed attempt he also used a device of the Ancients to overload the Stargate's capacitators so it would blow up the Earth.
He uses some kind of veil or advanced technology to hide his face, leading many fans to believe he has taken a host which is not human. This makes sense in many ways as he could get all that race's info, explaining why he can create shields to stop Tollan Ion cannons yet wants weapons that can penetrate them. Many believe he has taken one of the Furlings, understandable because of the high-level of technology and how the Furlings would be revealed in Season 6. I personally think that it is merely a race from outside of this galaxy whom we haven't met yet.
In Mythology
Anubis is a Greek name, he is known as Anpu in Egypt. He is also known as Ienpw or Yinepu. His name, unlike the other dieties, has no known meaning, it is thought to be either Royal Child or "to putrefy", both may be true as he was the Lord of the Dead. Osiris was also the Lord of the Dead and after Osiris's transition to the throne he was often known as Anubis's son. He has the head of a dog or jackal (or a mix of both). The black color of his head is symbolic of his being a funeral deity-rather than being the actual color of the jackals. He is amongst the oldest of the gods, even the oldest mastabas (tombs), have prayers to him carved in their walls. He is portrayed as being the one who invented embalming and is often known for his revival of Osiris to live as god of the underworld, a position that was Anubis's. Now he is the guide into the underworld who held the scales steady as the dead guys heart was weighed against a feather. If it was lighter then he would take them to Osiris, if heavy it would be fed to Ammit, a terrible demon who eats souls.
His geneology is quite vivid. In fact he has had multiple parents over time. His father was either Seth, Ra or Osiris. Which is odd since Osiris is also sometimes his son. His mother is either Nephthys, Heset or Isis.
Speculations
I find it odd that Anubis and Osiris share such a deep bond. Osiris reappears, disappears then not long after (less than a year) he starts working again to bind the Goa'uld together. Others believe that he is Sokhar. After all with the technology Sokhar exhibited he surely could have survived a small nucleur explosion. A fact helping this belief is that the same actor who plays Anubis, also played Sokhar. Others think that he is another race, such as the Furlings, Ancients or a yet to be encountered race. His location after all this time is also a matter of great debate. He was banished 1000 years ago and the system lords, as well as the Tok'ra believed him dead. They said he was banished because of a crime so great even the Goa'uld were shocked. One thing most people don't seem to notice is that Goa'uld have different moral values to humans. I mean for all we know deciding to go back into the water rather than taking a host could be a crime worse than...well it's bad... Most believe he's been sitting around in another galaxy gathering technology, with a few spies lurking around to see when the best time to return is.
His technology is the most heated debate. Firstly he has shields far superior to normal Goa'uld shields. They survived an ion cannon blast, they survived an attack from a Asgard ship, though i think the Asgard ship was the equivalent of a cargo ship with guns. But it also managed to destroy the Asgard ship. He has technology that even the Asgard have not seen, as well as technology of the Ancients. Many think that he somehow took the knowledge from the Ancient's database. Some suggest that he used a non-hosted Goa'uld to get the knowledge before blending, then healed damage to the host. This might explain the veil. Others suggest that he is the reason the database has anti-Goa'uld locks on it.
Apophis
In Stargate
For many years, Apophis has been the Tau'ri's main enemy. He has a habit of coming back to life when he's dead. He was the one who made the humans realize that the gate wasn't simply the doorway between two worlds, but was a connection between many worlds. He invaded earth to look for a host for his queen Amonet. This system lord has many enemies, including, Ra, Sokhar and Cronus. His first prime, Teal'c defected and joined the humans when they first arrived on Chulak. Chulak is the home of his jaffa. Apophis has borne the brunt of the jaffa rebellion and at one point he had lost almost all of his power. He rebelled against the system lords and amassed the greatest army the Goa'uld had ever seen. He took the troops of various other Goa'uld, including Cronus, Heru'ur and possibly Sokhar. He also managed to cloak his entire fleet and destroy Heru'ur's flagship. His host and Amonet's host, Sha're, who was once Daniel's wife, had a baby together. This is a harcesis, a host who has all the genetic knowledge of the Goa'uld. He was thought to be stolen by Heru'ur but in reality SG-1 had hidden him on Abydos. He was taken to Kheb by a handmaiden of Amonets. There he was protected by Oma Desala, a powerful alien being.
He was meant to have died after his failed attack on Earth. He brought two Cheops class warships, the other commanded by his son Klorel, who's host is Skara, O'Neil's Abydonian friend. SG-1 takes control of Klorel's ship with the help of Bra'tac. They steer near Apophis's craft, then board it and destroy the shield generators. Klorel's ship then explodes taking out the other ship. The second time Apophis "died" was when he crash-landed on a planet and begged SG-1 to give him protection from Sokhar. After he died from wounds caused by the crash they gave him to Sokhar. They later discovered him revived by a sarcophagus, disguised as first prime of a jaffa warden who guarded Sokhar's prison moon, Netu. The latest and hopefully last time he died was when his ship, crashlanded into his homeworld. There is no way he could have survived, seeing as there was no way off the ship and his shields couldn't possibly have survived the explosion. He wouldn't even have been in enough pieces for a sarcophagus to revive.
His homeworld is Delmak. The homeworld of his jaffa is Chulak.
In Mythology
Apophis is the Greek's name for Apep. Apep is not a god and was never worshipped. He is a serphant-like monster who lives in perpetual darkness, in the underworld. He is one of the sun god's main enemies. Each night he attacks the Sun God's barque it is a boat that carries the sun across the sky. The barque is often depicted as being defended by the gods Seth and Mehen. He would sometimes win a battle, causing a solar eclipse. However he may have won the battle but he always lost the war, since Ra always won in the end. He is wounded after each battle but he is always healed the next night. Eventually he is killed and Ra orders his body to be cut up and burned.