Allelujah Haptism is one of the four Gundam pilots (called Meisters) in Gundam 00. As a part of the organization "Celestial Being", he and the others stage interventions in conflicts throughout the world with the ultimate goal of eradicating all war. Through that goal comes the belief that the end will justify the means, and no one regrets those means more than Allelujah.
As the most kind-hearted of the four, Allelujah strongly dislikes the idea of killing others, but ultimately believes what Celestial Being is doing is the right thing. Pilot of the transforming Gundam, Kyrios, Allelujah is often called an unfit Gundam Meister because of this hesitation by another Meister, Tieria Erde. He is more than willing to wander from his mission in order to save the lives of others, regardless of the consequences he will have to face upon return to Celestial Being's ship Ptolemaios.
But even Allelujah has a dark shadow following him. As a victim of genetic engineering, Allelujah has an alternate personality called Hallelujah, who is everything his counterpart is not. Cold, sadistic, and maniacal, Hallelujah delights in violence and murder. Though Allelujah has most of the control over his mind and body, certain situations (usually involving quantum brain waves and/or the HRL pilot, Soma Peiris, also a victim of genetic engineering) cause Hallelujah to take control. In these cases, the two mirror personalities fight for control—but sometimes Allelujah doesn't regain full control until it's too late, leaving Allelujah to deal with the consequences of his counterpart's actions.