Sareth, a loner and a survivor, had a single consciousness within him. Unbeknownst to the Tok'ra his host Derrol had not spoken in several years which made him sympathetic to humans in a way that compromised his judgment. He was exiled by the rest of the Tok'ra during an escape when a system lord had discovered the secret Tok'ra base and began attacking, he sacrificed council members choosing to save newly blended Tok'ra which while considered to be noble was also to foolish to bring him along.
He was quickly marooned during the escape. And a councilmember gave him one Tok'ra cave crystal to build a shelter for himself to be used after the system lord would leave.
2 years later, a minor System Lord vying for power and status to be able to eventually attend the meeting Daniel Jackson infiltrated, believed the Tokra circled back to reoccupy the planet, discovered him on the planet. In his hubris, he accompanied six Jaffa to confirm this himself. As they approached Sareth, he decided to be as defiant as possible, standing his ground, ready to die, until a familiar voice finally returned with enough presence to say one word "Now!"
Quickly vanishing into foliage of a tree, one by one the Jaffa fell and the Goa'uld retreated back to his Alkesh Where's Sareth caught up with him before he could disable the automatic self-destruct completely and leave. Sareth prevented his departure, killing the Goa'uld I could do nothing to prevent the alkesh's destruction.
He ran to where the Stargate was buried screaming for Derrol name over amd over trying to get him to speak. He had found a new strength, a determination to redeem himself, and began to dig. Eventually he dug his way to the gate, using first the crystal, then his bare hands. To his surprise the positioning of the Stargate and its vortex trajectory, he was already half way there. He dialed Stargate after Stargate until finally coming upon a Phoenix team.