Most of Allelujah’s childhood is unknown. He somehow became an orphan and was used in the Human Reform League for experiments in the Human Reform League program. Experimentation led to a splitting of Allelujah’s personalities, bringing a darker side out of the usually gentle man.
A series of events led him and others to be left adrift in space, and out of survival the darker half took over and killed all on board. It is possible this is when Allelujah was discovered by Celestial Being.
Like all of the other Gundam Meisters, he was selected by Veda to be a Meister, and maintains this position.
There are two halves of Allelujah’s personality due to the enhancing of his brain. The two halves differentiate by the calling of the darker half, ‘Hallelujah’ as well as Allelujah’s hair covering the left half of his face to reveal a gold coloured right eye.
The dominant personality is Allelujah, a decidedly kind and gentle person. When the rest of the Ptolemaios crew went to Earth, he chose to stay and help with maintenance. He doesn’t like to kill, and it often brings up a confrontation with his other half, such as when he was about to fire upon the HRL’s Super Soldier Facility.
Hallelujah on the other hand carries a strong survivalist view, kill or be killed. He will do anything in order to survive. When Allelujah is in conflict over what he should do, Hallelujah will offer to ‘take over’ Allelujah’s body so he won’t be so morally conflicted. Hallelujah has gone as far as to claim he is the embodiment of Allelujah’s desires, taking action when Allelujah’s morals get in the way.