Theta

Creation
Theta was created along with his sister, Thorn, as a Historian - a biomechanical entity created to contain and distribute the entire history of Vale, based on the T.H.O.R.N. Project.

In the battle between Hannah Essentiae and Maximilian Essentiae, both were gravely injured, and their souls fused with the biomechanical bodies of the Historians. Thus, Theta and Maximilian Essentiae merged into a single identity.

In the Sacred Lands
The Historians, after merging with the original Essentiae Siblings, were deemed as too dangerous and powerful to be permitted free reign in Vale, and thus sealed into a section of Vale that the Essentiae line would come to worship as the "Sacred Lands".

Calamity Cascade
During the events of the Calamity Cascade, the seal on the Sacred Lands was broken, and thus the Historians were able to make direct contact with the Essentiae line, and assist them in defeating Zulu.