She is the Hydro Archon, the God of Justice; Regina of All Waters, Kindreds, Peoples, and Laws.
She is Furina's divinity and original self before being divided in two different beings, with Furina being her mortal half and the human she wished she could have been. She cursed Furina with immortality and tasked her with deceiving the people of Fontaine by taking her place as the Archon to the public while she sealed herself away alongside her Gnosis within the Oratrice Mecanique d'Analyse Cardinale housed within the Opera Epiclese. She did this for the sake of saving Fontaine and its people from a prophecy that foretold they would be dissolved by the Primordial Sea as punishment for the actions of the former Hydro Archon, Egeria.
At the end of Chapter IV Act V, Focalors reveals herself to the Iudex and then reveals her true plans before executing herself in order to destroy the Hydro Archon's Throne. This allowed her to return her powers back to Neuvillette, the Hydro Sovereign, enabling him to save the people of Fontaine by purging them of their "original sin", while also releasing Furina from her immortality and thus allowing her to finally be human and to pursue her own happiness.