She is not a god, instead, she is but an extremely old Fae who can transform into a dragon. Tirnoch was sealed tens of thousands of years ago by the ancient Alfar under the capital of the Winter Fae, Bhaile, in an area known as the Amethyn. It is unknown exactly why she was originally sealed, but ever since she has been seeking a way to free herself.
Due to her long imprisonment, Tirnoch not only desires vengeance upon the world for sealing her, but has gone mad. With the seal on her prison weakened, she, or possibly Gadflow, managed to contact one another. It is unknown whether she twisted his mind, or if his mind was already twisted, but Tirnoch swayed Gadflow to her service.
Using Tirnoch's power, Gadflow massacred the members of the Winter Court, and when the heroes of the Winter rose to avenge their lost king and remove Gadflow from his usurped throne, Tirnoch's power manifested and impaled them upon shards of Prismere. She also used her power to interrupt the Great Cycle to stop the immortal Fae who rose up against Gadflow and his Tuatha Deohn followers from resurrecting.
When the secret organization that the Fateless One and Alyn Shir worked for discovered the murmings of the Tuatha about their new goddess, the Fateless One volunteered to assassinate Gadflow and reseal the mad Dragon, despite the fateweavers' prediction he/she would only find death. Although all of the details are not known, he/she was killed on this mission, but this was not the Fateless One's end.
Although Gadflow proved a useful tool and would have eventually have been able to fully release her, Tirnoch chose another pawn to expedite her release into Amalur. Tirnoch broke the Fateless One free of the Tapestry of Fate and resurrected the Fateless One in Hugues' Well of Souls. This gave him/her the ability to change fate and to absorb the potential fates of others. Tirnoch knew that the Fateless One would eventually return to face her, full of tremendous power from the fates he/she had absorbed. It was Tirnoch's intention to then kill the Fateless One and use his/her accmulated power to free herself from her prison for once and for all.
Unfortunately for Tirnoch, the Fateless One's great power proved too much for her, and he/she was able to reseal her prison and prevent her from fully entering Amalur. This put an end to the Crystal War, and freed all of Amalur from the weave of fate.
- Her name is possibly a version of the term 'Tir Na Nog'. It's one of the famous, mystical places in the Celtic mythology. It is also close to the dragon 'Tiamat' from Mesopotamian mythology.
- Prismere is actually a physical form of Tirnoch's power on the mortal plane of Amalur.
- While her seal is strong, it is like any other crystal. But as she gets closer to her release, Prismere gains power and actually begins to grow, such as when the Fateless One was running through Bhaile and huge Prismere structures just grow from nowhere.
- It's very possible that the Tuatha learned of Allestar Tower through Tirnoch.
- The weave of fate appears to be tied to Tirnoch or at least her power has affected the weave, possibly as a curse of some sort against all living beings of Amalur; due in part that once she is defeated Agarth and other Fateweavers are no longer able to read the weaves of fate, though this might only be temporary.
- Another possibility is that Tirnoch was fated to be released and be victorious over the world and that the Fateless One defeating her broke fate.