Along with being a System Lord herself, Mat was a favored queen of the Supreme System Lord Ra though Mat saw herself as Ra's one true mate. She eventually left for a long time and found riches only dreamt of by the other Goa'uld: raw minerals to sustain the Goa'uld Empire for millennia and many precious jewels.
However, when Mat returned, it was to find that Ra had vanished. Mat eventually traced Ra to Abydos where she was told by Kasuf that they had delivered their tribute to Ra, he took it and left and then they saw a great light in the sky and Ra came to them no more. Following the death of Ra and later Apophis at the hands of Sokar, Apophis' queen Amaunet came to Mat for safe passage which she granted in exchange for information on Ra's death so that Mat could gain revenge. This event was witnessed by the Tok'ra Jolinar of Malkshur who had come to Mat's homeworld while undercover in Cronus' court. Amaunet, unaware that her host Sha're had tricked her, told Mat of how Colonel Jack O'Neill of the Tau'ri had been the one to kill Ra.
In 1999, in order to gain revenge upon SG-1 and O'Neill in particular, Mat placed a bounty on the team. Feeling that the most fitting revenge would be for Ra's killer to die in a test devised by Ra himself, Mat set the bounty so that the person collecting must get SG-1 onto the starting planet for the Trial of Ra. A Goa'uld mercenary named Tel'es posing as a Tok'ra succeeded and Mat herself took a Ha'tak to the twelfth planet of the Trial to meet SG-1 personally and kill them.
Upon arrival on the planet, SG-1 were captured by Mat's Jaffa and brought before Mat who briefly tortured O'Neill with her kara kesh. The enraged Mat explained her intention to gain revenge upon Ra's death by making them suffer through the Trial and was displeased to see that they had not suffered as much as she intended. Mat enjoyed tormenting the team, promising that Major Samantha Carter would become the host for one of her children and zapping O'Neill with her kara kesh multiple times as she told her story. Mat admitted that she was amused by the effect Teal'c's abandonment had on Ra's power and her enjoyment of the idea of Teal'c suffering an ending cycle of life and death before revealing that Amaunet had come to her.
Daniel attempted to trick Mat into revealing where Amaunet was, but she was just amused by the effort and considered making Daniel a host to one of her children. Mat taunted Daniel about his hopes of rescuing Sha're for Amaunet, claiming that nothing of Sha're remained within Amaunet and using the information that Amaunet had given her as proof. After Daniel noticed that O'Neill was preparing to make a move, he headbutted Mat, sending her back to where O'Neill was waiting. O'Neill wrapped his legs around Mat's throat and snapped her neck with a twist of his legs, killing her. After subduing SG-1, Mat's Jaffa removed her body to her Ha'tak to resurrect Mat using a sarcophagus.
As SG-1 reached the Stargate with the address and password needed, Mat arrived via ring transporter with four Jaffa. As her Jaffa faced off with O'Neill, Teal'c and Carter, Mat herself faced off with Daniel. Unafraid of Mat's threats, Daniel revealed to her that it wasn't just O'Neill that killed Ra but Daniel as well while the Abydonians rose up against Ra in rebellion and killed Ra's Jaffa. Mat refused to believe it, but Daniel told her that Amaunet had been lied to by Sha're and taunted her that her mate had died alone, abandoned by even his child slaves.
Enraged, Mat fired a blast at Daniel from her kara kesh, but he ducked the blast. As O'Neill and Carter closed in on Mat, Daniel hit her between the eyes with a plumb-bob, staggering the System Lord. As she was stunned, O'Neill and Carter tackled Mat to the ground, giving Teal'c the chance to snap her neck, killing Mat once more. Daniel then told O'Neill that Mat had to die beyond resurrection through a sarcophagus as with what she had learned, she posed too big a risk to Earth and Abydos. O'Neill and Carter dragged Mat's body in front of the Stargate as Teal'c dialed out. Mat's body was vaporized by the unstable vortex, ensuring that she could never be resurrected and her threat was ended for good. (SG1: "The Barque of Heaven")