Deus Trinity (ディース・トリニティ , Dīs Toriniti ) was the previous True Magic King. Long time ago, he was defeated by the wizard kings of the past. After that he waits for his resurrection within the Dante's Gate.
He was overthrown by some of the Malebranche 17 years prior to the start of the series.
After his defeat at the hands of Mira, Arsha had a bad feeling, as he might still revive. Later due to the curse placed on Arata's neck by him, he uses it to completely revive himself in another body vessel which used to be Gurafia, now which he is able to unleash his true power and his true abilities.
Deus Trinity's Thema is Caritas (愛情 / Compassion) of the Superbia Archive. But because Arbalishia tried to kill him, he managed to split his own Thema, survived, and even reached a higher level of his Thema even with just one character.
His Thema after his revival is Amore (Love). Reflecting this, his personality is twisted. He loves everything in the world, even his followers who tried to betray him. As an expression of that love, he wants to consume the whole universe.
The other half of his Thema, Sensus (Feeling), became Arata. For that reason he considers Arata his son.
As a Magic King, Deus Trinity can access three Archives: Superbia, Gula, Avaritia. But in his current weakened state without his core, and split from his true body, he can only access Superbia.