The original "builders of roads," the Ancients were once a race of advanced humans who were the original architects of the Stargate network. According to the Asgard, they moved on from our part of space long ago. In fact, the Ancients learned to ascend to a higher plane of existence when a great plague swept across the galaxy. Many died out, but those who learned to ascend shed their corporeal form gained a new sense of purpose.
The Ancients were once key members of an alliance of four great races in the galaxy, along with the Asgard, the Nox and the Furlings. The Ancients lived on Earth long ago -- or perhaps evolved on Earth itself, millions of years before our species did. One Ancient, Ayiana, was buried in ice in Antarctica for millions of years. Ayiana was left behind by the Ancients when they left Earth with the city of Atlantis, moving to the Pegasus Galaxy between five and 10 million years ago.
In Pegasus the Ancients seeded human life on many hundreds of worlds, as they had once done in our galaxy. They lived there for millions of years -- but then they came upon a planet where a powerful enemy slept. The Ancients had never before encountered a race with technology that rivaled their own. Awakened, the Wraith began feeding on the human-populated worlds, until only Atlantis remained untouched. The Wraith brought their powerful weapons to bear on the city, but the Ancients' shield held. Defeated, they submerged the great city into the ocean, and the last of them fled through the gate back to Earth. There they presumabley lived out their lives, telling stories that gave rise to the legend of the lost city. It is not known if these survivors ever ascended or had any contact with the ascended Ancients.
The Stargate network proves that the Ancients were one of the universe's most advanced species many millions of years ago, and had great minds into constructing a means to disperse many thousands of Stargates across the vastness of space -- even beyond our galaxy. They even had the technology to stop the movement of time itself (on several planets at once) and reverse it a number of hours, though they were unable to perfect that particular technology. Other advanced technologies left behind by the species include a device capable of altering human DNA to bring out advanced abilities, a healing device capable of restoring life and even animating non-living tissue, and more.
What is left of the Ancients, through gaining a higher moral center after ascension, is a hierarchy of somewhat omni-present, ethereal beings who feel they must remove themselves from interaction with all cultures beneath their non-corporeal plane. To merely interact with an individual beneath is breaking their law. Assisting a lower being in discovering ascension is punished by banishment. Meddling in circumstances that change the direction of a civilization is by far the most dire offense.
As punishment for breaking this law, the Ancients have been known to wipe out entire civilizations and abandon the one responsible in the midst of the mess they have caused (Ascension"). They have also forced (or tried to force) transgressors to descend back to corporeal form. Ancients are, by every means, capable of drastically altering courses of events at will. But, aside from their often cruel behavior, the Ancients do possess a high moral center that governs the majority's actions.
Ancients also have the ability to appear in human form or to reassume corporeal form permanently. Re-ascending then requires help from other Ancients.
Ascended beings have the ability to control weather conditions, turning a cloudless day into a hazardous lightning storm, and even using lightning as a weapon against enemies both in the air and on the ground.
Though the Ancients are not physically present, their actions have visibly altered the efforts of SG-1, among others. The Atlantis expedition is living in the Ancients' advanced city, which they were forced to abandon when the Wraith attacked thousands of years ago. Despite the fact that they are non-corporeal, they are still a powerful force to be reckoned with.
GOA'ULD
One of our galaxy's dominant species, the Goa'uld are serpent parasites that forcibly take human hosts, and possess a thirst for power and worship. They have enslaved countless worlds, using their inhabitants as hosts, soldiers, miners, and personal slaves.
Biology and Development
The symbiotic creatures are birthed from asexual mothers, Goa'uld queens. In the process every newborn symbiote inherits the genetic memory of the one before it. It is some time after their creation before the Goa'uld are capable of being anything more than helpless, squealing snakes. They must be fed a steady electrical current in an aquatic container placed where the people who serve the species are able to come and worship. Immature symbiotes are also incubated in pouches created in the abdomens of Jaffa, slave warriors in the service of the Goa'uld. It takes several years for a symbiote to reach full maturity and be ready to take a host.
Physiologically, the Goa'uld differ somewhat from symbiote to symbiote. Younger Goa'uld tend to be far whiter with twin black eyes. The older and more mature, the more gray or green the serpents tend to be. The majority of the species has four bright red eyes and swimmerets to suit them in an aquatic environment.
More mature symbiotes are capable of jumping significant distances, despite their form. Utilizing their powerful, four-pronged jaws, they burrow through the back of the neck (or through the soft tissue at the back of the mouth), wrapping themselves around the victim's upper spinal column and into the brain. Instantaneously the Goa'uld has control of the physical body, suppressing the original individual's consciousness.
Goa'uld symbiotes have incredible regenerative abilities, and, with the aid of sarcophagi, they are capable of living hundreds of thousands of years in the body of a human host. Once a Goa'uld is old enough to begin utilizing its healing abilities, it is implanted within the incubating pouch of a Jaffa in a ceremony known as the prim'tah. (During the period the Goa'uld is within a Jaffa, the term "prim'tah" can also refer to the infant symbiote itself.) The Goa'uld and its Jaffa are unable to communicate by conventional means, unless the Jaffa is in a deep state of kelnorim meditation. On this level of the subconscious, the Goa'uld receives vital information necessary to repair most illnesses.
History
The origins of the Goa'uld lie on the planet designated P3X-888. Long ago the Goa'uld learned how to infest and possess the Unas, another species native to that world, and learned to operate the Stargate on their planet and leave.
For an untold number of years the species was supposedly a dying race, unable to find hosts for their serpent form to exist within -- until a few thousand years ago, when the Supreme System Lord Ra, in a desperate pilgrimage through space to uncover his species' salvation, stumbled upon a planet of primitive humans: Earth. Ra harvested among the primitives and took the body of a young boy, seeding the rest upon different worlds in the galaxy as slave laborers.
The Goa'uld created Jaffa to serve them, whom the Goa'uld queens transformed from normal humans. The Jaffa became incubators for the larvae form as well as serving as the army for their entire populations -- greatly increasing the symbiote's chances of surviving and successfully taking over a human host. It is even possible that the Goa'uld occupied Earth in ancient times, posing as the gods and goddesses of various civilizations.
Culture
The Goa'uld society is feudal in nature. Their hierarchy is governed by the System Lords, a few dozen of the most powerful Goa'uld who are usually warring with one another for worlds and resources. Despite their cruelty, there are several rules that most strictly follow. For instance, it is forbidden for two Goa'uld, within their host bodies, to sexually reproduce a child. The human child, called a "Harcesis," possesses the Goa'uld genetic memory and is thus a great security risk to the Goa'uld.
The Goa'uld are opposed by the Tok'ra, a rebel subset of the species who, by nature of personal choice, differ from them on a philosophical level. The Tok'ra choose to co-exist with willing hosts, rather than take them by force. In recent years the Tok'ra have become increasingly problematic for the System Lords, whose desire to eliminate them is more desperate than ever before. The term "Goa'uld" is loosely used in that it is often mistaken as the primary definition of a symbiote; but the Tok'ra, who possess genetically identical creatures within, refuse to be known by the term "Goa'uld," believing it should only be used to define any symbiote demanding power and worship for themselves.
Without the Jaffa the Goa'uld are nothing more than parasites. To remain in control of the planets they have conquered, the Goa'uld pose as various gods from Earth mythology, so that the masses (people whose ancestors were transplanted from Earth thousands of years ago) will follow and obey.
Recently the Goa'uld have begun to show zero population growth, as the System Lords have been literally devouring symbiotes. Their desire for power and dominance, even over their Goa'uld brethren, is stronger than ever.
This is a complete race definition for both races.
Now, from SG-1 we know that the System Lords (as they call themselves) were also slain by RepliCarter in Reckoning Part 1.
They didn't even live to see their empires falls.
Only one System Lord lived through the whole thing and is now dead so that plainly states that the System Lords are all dead.
At this point one would normally through Anubis up but Oma, the Ancient, took care of him also.
So, this should show clearly that System Lords just plain suck and Ancients rule.
Thanks for reading,
Acronon
--by Miko Miko, for KonataChan, of animesuke. *borrows without permission, but with credits* ~_^
Now i am Ancient and I am proud 
