Kanan is the name of the Tok'ra symbiote which was implanted into Jack O'Neill.
Kanan was a Tok'ra who undertook several undercover missions on behalf of the resistance movement.
One of his missions was acting as a minor Goa'uld in the system lord Ba'al's most secret and heavily guarded stronghold (6.06 "Abyss"). Once there, he gained the trust of Ba'al's lo'taur, a young woman name Shallan. As Jack later explained to an ascended Daniel Jackson, Kanan grew to love Shallan. Through working with her over several months, Kanan was able to map out the entire complex and gain intelligence about all its defenses. He left Shallan at the stronghold, and his extraction was made without Ba'al's awareness of any infiltration.
Several months later, Kanan acted as an operative aboard one of Zipacna's motherships. He barely escaped after a battle with System Lord Yu's forces. Kanan's host was apparently injured beyond the symbiote's ability to repair. The Tok'ra were able to retrieve the symbiote Kanan, but could not save the host.
Simultaneously, in Antarctica, Jack O'Neill had been subjected to a plague for which there was no known cure (6.04 "Frozen). Although others subjected to the illness were saved by the Ancient Ayiana, she perished before she could save O'Neill. Thoran of the Tok'ra offered the option of a temporary blending with Kanan. Terminally ill, O'Neill was approached by Carter with the Tok'ra's offer. At first O'Neill resisted, prefering death to being "blended", but Carter explained the symbiote had vital information that would help their allies. Further the Tok'ra would look for another host for Kanan, and if none were found, the symbiote would sacrifice itself rather than remain in an unwilling host. Therefore, the condition would be temporary, and O'Neill relented.
Thoran and the Tok'ra brought O'Neill to their base and Kanan was implanted. Because most of the symbiote's energy was used in healing the Colonel from his weakened and ill state, no "true blending" occurred. When Kanan and Jack later parted ways, O'Neill could later only recall vague memories of the symbiote and did not retain the protein marker to be able to run Goa'uld technology or sense another symbiote's presence.
Kanan was able to able to debrief the Tok'ra about his most recent information and provide the key intelligence they needed. Kanan/O'Neill remained at the Tok'ra base until a new host could be found (6.05 "Nightwalkers").
Although O'Neill may not have retained much about Kanan, O'Neill's personality and memories seem to have made an impact on Kanan. One of O'Neill's strongest held beliefs was that "no one gets left behind." This mantra apparently became a siren song to Kanan, and, using O'Neill's body, Kanan snuck out of the Tok'ra base to return to Ba'al's stronghold and retrieve Shallan (6.06 "Abyss").
Kanan and Shallan made their way to the Stargate with Ba'al's Jaffa in hot pursuit. As they approached the DHD, Kanan pushed Shallan towards cover to hide until he could activate the wormhole. However, as he dialed, he was wounded by a staff blast. Kanan's motives are unclear for his next action: it could have been a combination of various reasons, including but not limited to, protecting the Tok'ra movement, mistakenly thinking it was saving O'Neill from torture since the host knew nothing, delaying Ba'al gaining knowledge, or even as Ba'al himself conjectured, as an act of cowardice. In any event, Kanan left O'Neill's body and scurried into the undergrowth.
Without a new host or appropriate environment to sustain the symbiote, Kanan would have died. It is unclear if that is what happened, but Kanan was never seen or heard from again. His actions were later vilified by Selmak (6.09 "Allegiance"). Selmak's host, Jacob Carter explained Kanan's actions using O'Neill broke one of the Tok'ra's highest laws and Selmak was sickened by it. However, Selmak noted Kanan's reasons were good. O'Neill was not as sanguine about the experience and it sealed his distrust of the species.
--DeeKayP 19:55, 2 Sep 2004 (PDT)