Baal-berith was the god of a Canaanite city who later came to be viewed as a demon by Christian demonologists. In the Book of Judges, his temple was destroyed after the king Abimelech quelled the rising of his subjects. In Rabbinical literature, the idol Baalberith which was worshiped by the Hebrews after the death of Gideon was identical with Baal-zebub and was worshipped in the shape of a fly. The name berith means "covenant".
Belberith is the demon that inherited the biggest part of the original Bel's power, and also his memories. As such, he carries on Bel's lust for revenge against God. At the time of the game's happenings, he already has absorbed a number of other Bel demons, and has both Jezebel and Belzaboul under his command (even if the latter only obeyed him as part of Lucifer's orders). He is worshiped by the Shomonkai as a god, and their belief in him gives him power.
Belberith is driven by revenge against God. While powerlust is also a part of Belberith's personality, he will gladly forego his own desire for power if it means the new King of Bel will continue his crusade against God.
He is designed as a mishmash of several preexisting demons (Baal, Bael, and Belphegor) fused to a fleshy mass with many spider legs protruding from it.
Belberith retains his role in Overclocked, except that now he is fought as the final boss on Yuzu's 8th Day. It is revealed by Naoya that he arrived while the party escaped the day before, resulting in the government calling off their final option (as the UEM Field would simply empower him).
During the last battle, Honda asks him for power in order to resurrect his son. Belberith initially agrees, and calls in Baphomet to assist him. When the player defeats Baphomet, Belberith responds to Honda's further requests to see his family again by killing him.
Belberith has leftover data from the first game, seen as a compendium entry:
"One of the 72 demons of the Goetia and the duke of Hell. Said to be derived from Baal-Berith or Baalberith, a god of the Canaanite city mentioned in the Old Testament, later known as a demon in Christianity. According to Sebastien Michaelis, Baalberith tempts men to blasphemy and is an adversary to St. Barnabus. Before his fall from grace, he was prince of the cherubim."
On Yuzu's 8th Day in Overclocked, part of Belberith's speech is left untranslated in Japanese.
In Devil Survivor 2, Belberith, Jezebel and Beldr have leftover data. All three can be registered in the Compendium with full explanations, and are next to Belial and Beelzebub in the game's list. This may imply that all of the Bel demons were planned to be in the second game, perhaps as bonus bosses, but only two were fully added to the final game. Belberith is lacking an image in his status page, but functions more or less the same as he did in the first game.