Kanan was a Tok'ra operative. During one of his earlier missions he had worked undercover as a minor Goa'uld in Ba'al's service, and he had used Ba'al's female lo'taur, Shallan, to access information about Ba'al's secret outpost for weapons technology and gravity field generators. During his last mission he had been an operative aboard Zipacna's fleet, and managed to escape during a battle with Lord Yu's forces. Although his mission objectives were completed, his host was mortally wounded and died before he was able to reveal details of the intelligence from the mission. The symbiote lived on, in dire need of a host, and when O'Neill faced death from the virus contracted from Ayiana, O'Neill agreed to become a temporary host in order to cure the virus and access the vital intelligence. However, a true blending never occurred. Kanan blocked his knowledge from O'Neill, and took control of O'Neill's body without his consent. Through his exposure to O'Neill's code of honor, Kanan was driven to return to Ba'al's outpost to rescue Shallan, but the rescue was unsuccessful, and the symbiote fled O'Neill's body to avoid capture by Ba'al. Kanan is presumed dead, and O'Neill became Ba'al's prisoner, with no memory of what had brought him there.
Cross Reference: Ba'al, Lo'taur, Jack O'Neill, Shallan, Thoran, Tok'ra
Episode Reference: Frozen, Abyss