Sigyn was engaged to an Asgarian god and one of Odin's Crimson Hawks, Theoric, when she captured the attention of Loki. He proposed to her, but Sigyn denied his affections and proposal. Not taking no for an answer Loki kills her finance, takes his form, and marries Sigyn undetected to even the likes of Odin , who married the two. When Sigyn's husband reveals his true identity, Odin attempts to annul the marriage, but Asgardian law forbids even the High Father to do so. Thus, Odin could only exile Loki, but Sigyn, in tears, accepts the marriage and follows him. Impressed, Odin declared Sigyn the Goddess of Fidelity. During their marriage, Sigyn mothered two sons, Narvi and Váli, with Loki, although both of them died young.
Major Story Arcs
Devoted Wife of Loki
When Loki killed Balder, he was punished by Odin by being chained to three rocks and having a poisonous viper drip venom onto his face. Sigyn did not abandon Loki as she was granted permission by Odin to catch the venom in a bowl before it reached Loki. However, she would have to leave periodically to empty the bowl. During the times that she emptied the bowl, the venom would drip onto Loki's face, for which he blamed on Sigyn. When Loki was freed from the rocks, he deserted his wife. On more than one occasion, he has returned to save her life. The most prolific being when he transfers his spirit from that of his restrained body to Thor in order to save Sigyn's life, after she is about to be killed in order for revenge against something Loki has done. He has referred to her as 'The love of his immortal life'.
Fourth Coming of Celestials
When the Asgardians were preparing for the Fourth coming of the Celestials, Sigyn was one of the Asgardians gods who assisted Gaea save the Earth by offering the Young Gods. She was given the task with other goddesses to guard the Young Gods underneath the Earth for 20 years.
Despite being previously deserted by Loki and having an tumultuous relationship, Sigyn continued to be the devoted wife. During a time that Loki was imprisoned within a tree, Sigyn was angered by Odin's imprisonment of Loki. She followed Odin to Earth and placed the real body of Donald Blake in suspended animation within Mount Wundagore as a bargaining chip to free Loki who was supposed to Thor's Earthly identity. Unfortunately, she accidentally killed the real Blake when a her spell to capture him backfired. To cover her mistake, she used her powers to create a doppelganger of Dr. Donald Blake. However, she accidentally left her wedding band in Mount Wundagore. Years later, Thor found the duplicate Blake and thought Loki was behind the ruse after finding the wedding band. Sigyn bound Loki's spirit to a suit of armor, as Loki was disembodied during this time, to battle against Thor. Once Loki's armor was badly damaged, Sigyn told Thor the truth and that she meant him no harm.
Her death was mentioned in Avengers: Roll Call #1 She was either killed or died of natural causes.