Gairwyn is an inhabitant and leader of the planet Cimmeria. Her people, the Cimmerians, are descendants from a Norse tribe, originally located on Earth thousands of years ago. Gairwyn and the rest of her people have worshiped the Norse god Thor for centuries, believing that he gave them the tools of civilization and that he protects the planet from the Ettins.
When Teal'c and Colonel Jack O'Neill were scooped up by Thor's Hammer, she helped Captain Samantha Carter and Dr. Daniel Jackson find Kendra to take them to the Labyrinth. Gairwyn was helpful to the pair and was somewhat excited to interact with visitors from Midgard, the old world. Gairwyn was present at the destruction of Thor's Hammer, which she agreed was necessary to free Teal'c. SG-1 later gave her and Kendra a Sagan Institute Box to contact the SGC should they ever need their help. (SG1: "Thor's Hammer")
Almost a year later, the Goa'uld Heru'ur arrived on Cimmeria and proceeded to subjugate the planet. Acting on the instructions of Kendra, who had been killed in the fighting, Gairwyn sent the Sagan Institute Box through the Stargate to Midgard, but was careful not to step through the gate herself. The SGC sent a M.A.L.P. through the Stargate to investigate, and Gairwyn pleaded with SG-1 through the device.
Upon their arrival, Gairwyn guided the team to a safe place and explained the situation, and gave Carter some of Kendra's Goa'uld equipment. She guided Carter and Dr. Daniel Jackson to the Hall of Thor's Might, which they hoped would contain weapons to assist in Cimmeria's liberation. Within the hall, the group was forced to face Test of Worthiness. During the first test, Gairwyn interpreted the shaking of the beam she was on as a sign that Thor wished for her to die, but Carter and Jackson convinced her that it was meant to test the group's morality. During the second test, Gairwyn assisted Daniel in translating the Norse runes, but lacking an understanding of complex mathematics, was unable to help with the rest of the test. When they completed the challenges, the hologram of Thor changed from a boisterous, armor-clad human warrior to that of his true form: a diminutive soft-spoken grey alien. Shocked and dismayed, Gairwyn questioned the hologram, but Carter calmed her down, explaining that it was simply a recording. Thor, however, responded and explained that he was in fact speaking with them in a live transmission from his flagship. When he learned of SG-1's interference in Cimmerian affairs, Thor ejected Carter and Jackson from the Hall and brought Gairwyn aboard his flagship, the Biliskner, a powerful Asgard Mothership.
After the Biliskner had dealt with Heru'ur, Thor beamed Gairwyn back to the planet. Her faith seemingly restored, Gairwyn relayed a number of messages from her god. She told SG-1 Asgard held humanity in high regard and had visited Midgard many times, but that not even the Tau'ri were ready to deal with them as equals. Thor would leave behind an Asgard teacher to help the Cimmerians rebuild, and would also install a new Hammer to protect them from the Ettins, with an exception for Teal'c. Gairwyn then assured SG-1 that they would always be welcome in Cimmeria. (SG1: "Thor's Chariot")