Thessalia grew up in House Dvora (PROSE: The Book of the War) with the Imperator, and in adulthood they shared a common philosophy as well as a romantic attraction, (PROSE: The Return of the King) as speculated by historians in Faction Paradox. She was later appointed chatelaine of the barren House Ixion. (PROSE: The Book of the War)
A week before the Imperator's ascension to the Presidency, he visited Thessalia at House Ixion. Wanting someone with a similar philosophy in his administration, the Imperator created the Order of the Weal for Thessalia to lead, knowing that he might turn against her one day. At the time, she kept an oracle in House Ixion. The meeting was recorded on a registry.
Indeed, Thessalia and the Order did assess the Imperator as a threat, and she shot off his jaw to prevent him from speaking (PROSE: The Return of the King) while she denounced him to the ruling Houses. However, she played no part in his trial and execution, (PROSE: The Book of the War) instead going into seclusion. Some who knew her at the time said she committed suicide by putting a gun in her mouth in an attempt at self-improvement.
After the fall of the Imperator, the girl who would become Larissa and the boy who would become Lord Yellow Dog of the Thirty-One Cuts were moved from House Dvora to Ixion. Their playing brought Thessalia wrath's upon them, and Larissa was terrified of her. At the time, Thessalia appeared as an old, hunched crone, with shambling footsteps and jangling keys on a metal ring on her belt. (PROSE: Newtons Sleep)
As chatelaine of the Order of the Weal, Thessalia directly controlled all operational matters alongside her heir, whose identity shifted as Thessalia's allegiances unpredictably changed. She had a bodyguard of myrmidons. (PROSE: The Book of the War)
Thessalia grew younger, taller, and healthier; Larissa speculated this was during the worldquake or the goblin infestation. She recruited Larissa to become her mnemonic, claiming she distrusted registries after the Imperator's were used against him in his trial. She used Larissa as her living diary and called her "my little book". (PROSE: Newtons Sleep)
The Chatelaine considered all oral mythology to be a lie designed to obscure or excuse contemporary political activity. She held that the only truth was what one could directly sense, intuit, or reason. (PROSE: The Book of the War)
She identified five organisations on the Homeworld, mainly the most extreme intervention groups, that might encourage an aggressive foreign policy for their own profit, as well as thirteen potential external aggressors who might be the Great Houses' future enemy. (PROSE: Newtons Sleep) She predicted that the enemy would be motivated unambiguously by a racial-survival agenda and mainly concerned with maintaining the integrity of its own history. She also expected the first attack on the Homeworld to be aimed at its noosphere, with physical fighting only occurring in the final stages of the war. In anticipation of this, she commissioned the babels as a defence for the Homeworld's noosphere. (PROSE: The Book of the War)