Teal'c is a Jaffa, who once served the System Lord Apophis in the capacity of First Prime and then later joined SG-1.

Teal'c's father had served as the First Prime of Cronus, a rival System Lord. When his father retreated in a battle that could not be won, Cronus executed him for failure. Teal'c and his mother fled to Apophis' territory, and Teal'c joined the Serpent God's army in the hopes of one day encountering Cronus and avenging his father's death. Under the direction of Bra'tac, the then First Prime, he learned the ways of a warrior and rose in the ranks to become Apophis's new First Prime.

His interaction with Bra'tac and his own personal experiences led him to doubt the divinity of the Goa'uld. This was further reinforced when Valar, a close friend of Teal'c's, failed Apophis in an important battle. Apophis ordered Teal'c to kill Valar but instead he faked his death. The failure of Apophis to see through the fake confirmed his belief in the falsehood of the Gods.

In the first episode of the series, Teal'c defected and returned with SG-1 to the SGC. Teal'c believed that the "warriors" of the Tau'ri (Humans) presented an opportunity for the eventual defeat of the Goa'uld.

Around four years after he joined the SGC, Teal'c was captured in battle by Apophis, and brainwashed into believing that he was still the First Prime of Apophis, and that his friendship with the Tau'ri was a ruse. SG-1 managed to recapture Teal'c, and killed Apophis once and for all in the process, but the damage was still done. It took Master Bra'tac and the Rite of Mal'shuran to restore Teal'c's true beliefs. Teal'c later used this incident to bond with his son, who was similarly brainwashed in the Season 2 episode Family.

Teal'c's main drive throughout the series is to topple the Goa'uld regime and bring freedom to all Jaffa. After several battles with the Goa'uld, during which they suffered several highly visible defeats, an organized Jaffa resistance eventually came to fruition. In The Warrior, the First Prime of a minor Goa'uld, Imhotep, organizes Jaffa of several other Goa'uld into a small army. Though this gathering was only subterfuge by Imhotep, Teal'c and SG-1 were able to save the bulk of this resistance from slaughter by moving them to the Alpha Site. However, the Tok'ra later took refuge at the Alpha site as well and soon clashed with the ideals of the Jaffa Resistance. Teal'c, Bra'tac, and SG-1 could not quell the tension between the two factions so they simply went their separate ways. Yet, these many events permanently planted the seed of resistance and the ranks of the Jaffa Rebellion have increased.

About six years after Teal'c joined the SGC, Teal'c and Master Bra'tac attended a summit of Rebel Jaffa. The Rebels were massacred by Jaffa loyal to the Goa'uld, and only Teal'c and Bra'tac survived, with a single Goa'uld symbiote between them. Teal'c transferred the single symbiote between the pair of them, and eventually began to hallucinate, slipping between visions of his life in the SGC and a fictional life where he was an ordinary human firefighter. With the help from an Ascended Daniel Jackson, Teal'c kept himself and Bra'tac alive long enough for SG-1 to rescue them. Jacob Carter arrived at the SGC with a modified version of the Tretonin medicine (Season Six Episode Cure). Both Teal'c and Bra'tac now sustain themselves with the use of Tretonin, and the drug has become instrumental in liberating Jaffa from physiological reliance on Goa'uld symbiotes (though some Jaffa simply see this as transferring reliance from the Goa'uld to the Tau'ri).

Teal'c and Bra'tac took an influential role over the free Jaffa and eventually mobilized and led them to victory over the Goa'uld at Dakara, where a new Jaffa democracy was established. From the day of victory on Dakara, Teal'c and Bra'tac were hailed as "blood kin to all Jaffa."

He is currently a member of the Jaffa High Council and a leader of the liberal faction that supports Tau'ri-based representative democracy for the new Free Jaffa Nation, opposed to the traditionalist faction headed by Gerak. Since Gerak's death, it would appear that Teal'c has supported Bra'tac as an interim leader before a type of government is solidified. However, since the destruction of Dakara by the Ori, and Bra'tac's news of the Jaffa being scattered by the destruction of their power base, his current standing among them is unknown.

Source | Wikipedia.org