Goa'uld

The Goa'uld are a fictional parasitic alien race in the Stargate universe. They look like snakes, but they normally insinuate themselves into the brains of large animals, which they can control. They find humans particularly suitable as hosts. A singular Goa'uld is sometimes referred to as a symbiote.

On their native homeworld (known only by its SGC designation, P3X-888) the Goa'uld begin their lifecycle as relatively helpless aquatic larvae, spawned in large numbers from a Goa'uld queen. Those that survive to maturity develop elaborate fins that allow them to spring powerfully out of the water to burrow into a suitable creature's neck. The Unas evolved on the same world and were their original favoured host. Once a Goa'uld takes a host it is not easy for it to switch to another; it loses its fins and its body appears to atrophy significantly. Starfaring Goa'uld developed an alternative lifecycle, modifying a race of humans into Jaffa to act as incubators for their larvae. This was apparently done both to produce powerful warrior servants and to improve the ability of the larval Goa'uld to take a human host on maturity; Goa'uld larvae that grow up "in the wild" have only a fifty percent chance of being able to take a host whereas Jaffa-reared larvae are universally capable.

Most Goa'uld bear the names of classical gods, excepting the Norse gods, and especially those of ancient Egypt. In fact, the term Goa'uld means "Children of the Gods". There is still debate as to whether the Goa'uld assumed the names of Egyptian gods already in existence or whether Egyptian mythology stems from the Goa'uld's one-time domination of (ancient) Earth. The most powerful Goa'uld are called System Lords. They rule whole planets, lead huge armies of Jaffa warriors, and maintain fleets of powerful spaceships that resemble pyramids. Major Goa'uld System Lords included Apophis, Ba'al, Heru'ur, Hathor, Osiris, and Anubis many of whom have since died during the progression of the show. The most powerful System Lord was Ra — until the Tauri killed him in the 1994 movie Stargate. The Goa'uld term for the Stargate is "Chaapa'ai".

Goa'uld are able to pass their memories directly to their offspring through genetic memory. This can also occur when a pair of Goa'uld hosts mate and produce an offspring; the resulting child is biologically human but possesses the knowledge of the Goa'uld. Such a child is known as a Harcesis and is considered an abomination by the Goa'uld, who do not normally choose to produce them.

A Goa'uld-occupied host usually speaks in an eerily flanged, bass-augmented register (except when allowing the host to act freely, or imitating a normal human); extreme emotions in the Goa'uld cause the host's eyes to briefly glow. The Goa'uld instill increased strength and remarkable healing abilities in their hosts; the host shrugs off injuries that would incapacitate or kill most humans, and experiences a lifespan of centuries (which System Lords commonly extend almost indefinitely through the technological means of a sarcophagus). Being a host is regarded as a living hell and those hosts who have been under the control of Goa'uld for extended periods of time are widely suspected of having gone insane. Most of the Goa'uld killed in Stargate SG-1 have been in a host at the time, who died along with them. The death of the host in these instances has generally been considered merciful. If any attempt is made to forcibly remove a Goa'uld from a host the Goa'uld may release a deadly toxin into the blood stream of the host, killing the hapless individual. Nevertheless, the Tollan possessed the technology to safely remove a Goa'uld, and the Tok'ra are able to accomplish this in some cases as well.

A subculture exists within the Goa'uld called the Tok'ra (Meaning literally "Against Ra"), a group of Goa'uld who are opposed to the ways of the System Lords. Descended from the Goa'uld Egeria, they share the desire to have a truly symbiotic relationship with their hosts. They are a resistance movement which attempts to overthrow the System Lords' tyranny. Although biologically the same species, Tok'ra prefer to not be referred to as Goa'uld.

Goa'uld symbiotes can be refined and used as a drug called Tretonin. When used, the user gains many of the same health advantages having a Goa'uld symbiote allows. However, use of the drug also kills the user's immune system.