Once an underling of the System Lord Camulus, Qetesh subsequently took control of Vala Mal Doran, suppressing Vala's own original consciousness while allowing Qetesh complete control of Vala's body.
With Vala as her unwitting host, Qetesh ruled over at least one world, P8X-412, where she forced the inhabitants to mine the planet's sparse Naquadah deposits. When quotas were not met, she instituted both mass executions and mass torture.
She has also been at war with Ba'al (although it is not stated precisely when) and killed, according to him, 10,000 of his best Jaffa. She also declared war on the Goa'uld Athena which waged a little but they came together to find the Clava Thessara Infinitas.
The Tok'ra eventually captured Qetesh, forcing the symbiote out of Vala's body which caused Vala's original consciousness to be restored. Qetesh was presumably killed following the extraction if she survived it. (SG1: "Prometheus Unbound", "The Ties That Bind", "The Powers That Be", "Insiders", "Memento Mori").
Like all other Goa'uld, Qetesh was power-hungry, ruthless and extremely arrogant.
She was also devious, capable of betraying those who followed her and even had a habit of double-crossing others, all for the sake of fulfilling her own agenda as well as claiming power for herself.
She also appeared to possess a sadistic nature of some sort as after stabbing Ba'al through the chest with a sword, Qetesh didn't kill him immediately, instead choosing to keep him alive for a prolonged period of time so that she could torture him via a hand device and gain the information she needed.
In an alternate timeline created when Ba'al changed the timeline so that Stargate Command and SG-1 never existed in the first place due to the Stargate never reaching the United States, Qetesh was his queen, having never been removed from Vala Mal Doran's body at all. Qetesh was as duplicitous as she had been in the original timeline, however, and being suspicious of his knowledge of Earth, she conspired with Cronus to kill Ba'al and seize his throne which Qetesh did by stabbing Ba'al and also torturing him with a Goa'uld hand device. She learnt about his time-travel device beforehand and she traveled to the planet where it was located, while her fleet bombarded Earth from orbit. Her Jaffa killed Dr. Daniel Jackson and Colonel Samantha Carter and mortally wounded Teal'c, but Colonel Cameron Mitchell had managed to escape through the Stargate into the past. Qetesh transported down to the planet containing the time-travel device but was killed by the wounded Teal'c when he detonated a grenade. The explosion killed her and any remaining Jaffa guards while also destroying the time-travel device. (Stargate: Continuum)
Vala reflects on her time as Qetesh, revealing that Qetesh was one of Ra's daughters and lost a lot of power when he was killed over Abydos. In the alternate timeline, Qetesh once again takes Vala as her host and makes Cameron Mitchell her First Prime after they travel to one of her worlds while seeking to repair the timeline. Using Mitchell and Vala's knowledge, Qetesh managed to get herself into a position of power with Ra to the point that he let her lead the attack on Earth in 1947. Qetesh planned to use Earth's atomic bombs to kill Ra, having ensured that if he died she'd be able to take his place but Mitchell and Vala had been plotting against her during the two times she was pregnant and had to give control to Vala to ensure the safety of both Qetesh's babies. Mitchell aided SG-1 and An in fighting against Qetesh and she was killed when An beamed an atomic bomb on her ship, blowing it up, followed by Ra's. As Ra, Qetesh and Ra's First Prime were dead, Mitchell was able to use his position as Qetesh's First Prime to bring an end to the attack on Earth. (SG1: "Roswell")
Behind the scenesEdit
In the end credits for Stargate: Continuum, the name Qetesh is misspelled as "Quetesh".