Tanith was the name of the Goa'uld housed inside Chulakian priestess Shan'auc which soon matured. It chose to be named Tanith and was implanted in Hebron of Paraval. Unfortunately, in spite of Shan'auc's hopes that the Goa'uld were wrong, Tanith later fully emerged, taking complete control of Hebron's body before he murdered Shan'auc.
For the next two years, Tanith would become a huge thorn in the side of SG-1, particularly Teal'c up until Tanith's death at Teal'c's hands in 2002.
Convinced that she had swayed the immature symbiote she carried to a new philosophy, Shan'auc of the Red Hills took this information to the Tok'ra to procure a willing host for it. As a former lover of Teal'c, Shan'auc offered hope that the Goa'uld threat might be lessened through such contact.
However, Tanith had been deceiving Shan'auc all along and after implantation, Tanith murdered her by crushing her new prim'ta, a fate that had befallen Teal'c's own father years before. The Tok'ra suspected Tanith's crime, however, they played along with Tanith, allowing the symbiote to maintain control of its host body as a means to disseminate disinformation to the Goa'uld. (SG1: "Crossroads")
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Unfortunately, their plan failed when Tanith, having been aware of their plan, decided to take matters into his own hands. He faked being dead before overthrowing two Tok'ra guards who had arrived in to investigate before escaping which also triggered a huge search for him with Teal'c leading the search.
On the hills of Vorash while hiding out of sight, Tanith retrieved a long-range communication device which he used to contact Apophis, informing the System Lord of the Tok'ra's location.
A while later, Tanith ended up meeting with two of Apophis' Jaffa with one Jaffa stating that Apophis was grateful to Tanith for his service with Tanith stating there was one more thing Apophis could be grateful for.
With the help of Apophis' Jaffa, Tanith was able to capture Teal'c although he was left injured after Jack shot Tanith in the arm.
To prove his loyalty to Apophis, Tanith later presented Teal'c to Apophis as a "gift" and as a result, Apophis brainwashed Teal'c into becoming his First Prime once again which effectively also led the Jaffa to believe that he had been a spy for Apophis for nearly five years which was also the time Teal'c had been on SG-1 which effectively ended up turning Teal'c against his friends, Colonel Jack O'Neill, Major Samantha Carter and Dr. Daniel Jackson.
For an unknown reason, Tanith abandoned Apophis' ship in an escape pod before the supernova which he'd had no knowledge of occurred, effectively resulting in Tanith abandoning Apophis forever. (SG1: "Exodus", "Enemies")
After Apophis was killed, Tanith offered his services to a more powerful Goa'uld, Anubis. Arriving at Tollana with a mothership protected from the Tollan Ion cannons, Tanith forced this advanced culture to build powerful weapons that would penetrate solid matter such as the iris shield at Stargate Command in exchange for their continued survival. Tanith attacked the planet in the end, and a hurried transmission through the Tollan long-range communications device informed the Tau'ri that only a few Tollan had escaped and defenses were failing before cutting out completely. (SG1: "Between Two Fires")
Two years after Shan'auc's death, in 2002, Teal'c finally succeeded in avenging her when SG-1 was scouting a Goa'uld base on Memphis. He killed Tanith by shooting his Al'kesh's cockpit with a Staff cannon, causing it to crash right on top of the Dial Home Device as Teal'c was passing through the wormhole. The impact prematurely disengaged the transmission, leaving Teal'c's energy signature 'stalled' in the wormhole until the transmission could be continued. Emergency measures were taken, including borrowing the Russian DHD after a heartfelt plea from Dr. Daniel Jackson, to regenerate the transmission and retrieve Teal'c before another wormhole was established, thus saving the Jaffa's life. (SG1: "48 Hours")
Tanith was a sly, cunning and ruthless Goa'uld. He was also very sadistic, often mocking and tormenting his victims to some extent.
He also appeared to be a sadist when he mocked and tormented Teal'c over Shan'auc's murder.
Unlike his fellow Goa'uld, Tanith had no qualms or regrets over abandoning or deserting his current Goa'uld master, all for the sake of joining the service of another Goa'uld, one far more powerful. He was also deceptive and capable of double-crossing those who work for him which was demonstrated by his actions against the Tollan.
In addition, Tanith was psychopathic, displaying little or no remorse whatsoever for his crimes.
Despite his nature, Tanith, like many of his fellow Goa'uld, was arrogant and proud but not very smart, which eventually proved to be his key weakness and which eventually led to his downfall and death.
- Like many underlords, Tanith has been seen using a silver hand device.