From Halopedia, the Halo wiki
Parabum (nicknamed Big Boy by his human prisoners) was a Jiralhanae Chieftain commanding the Covenant ship, the Valorous Salvation, as of late 2552. He landed on the human colony of Beta Gabriel, and led a slaughter of the population. He was a member of the Rh'tol skein, as denoted by the "-um" suffix in his name.
The pack which crewed the Valorous Salvation was in fact the product of two separate packs which had recently been merged by the Covenant leadership. The two clans were ancient enemies that had fought even before the massive civil war that had knocked the Jiralhanae back to a pre-industrial state. Naturally, this led to tensions between the two factions within the pack. One clan, led by brothers Ceretus and Maladus, felt themselves to be the more intelligent faction of the pack, and their devout religious beliefs were more in line with those of the Prophets. The other faction, led by the pack's Chieftain Parabum, believed only in muscle and tradition, and used relics in more opportunistic and disrespectful ways.
During the Fall of Reach Parabum exhibited cowardice when he ordered the ship to retreat from the massive attack and instead landed on the nearby Beta Gabriel. When they first arrived on the planet they hunted the humans they found there and feasted like never before. Ceretus and Maladus didn't even bother using their Paegaas Workshop Spikers, as they had more fun killing them with their bare hands. As the number of humans dwindled, they ate the Unggoy who had been aboard the ship, and Parabum instituted limits on hunting and eating the humans.
Shortly afterward, Maladus snapped and challenged Parabum over his cowardice and abandonment of their duties to the Covenant. However, Parabum was stronger and mercilessly pummeled him into submission before tearing his throat out with his teeth. This only served to further enrage Ceretus.
After capturing Connor Brien and returning to their camp after Brutes of Ceretus's hunting party killed one of the captives, Hague, for fun, however when Parabum's hunting party returned he was annoyed and embarrassed Ceretus in front of the others.
Ceretus then began plotting to overthrow Parabum, but he had no hope of beating the chieftain in a direct challenge. Instead, Ceretus tried to convince another Brute, Hammadus, who was the only one strong enough to defeat Parabum. He did so by using Hammadus's brother Facius, and arguing that they needed to overthrow Parabum, return to the Covenant, and beg the gods for forgiveness or else face damnation.
Ceretus got Facius to try to convince Parabum to return to the Covenant, with Hammadus promising to protect his brother. When Facius spoke to Parabum however, the chieftain responded by saying that there were no gods, causing Ceretus to erupt with pious indignation. Parabum then killed Ceretus with his gravity hammer. Connor Brien then shot Parabum and Hammadus with his tranquilizer gun, knocking them unconscious. Pandemonium reigned and many of the human prisoners attempted to escape, however one woman named Nixaliz chose to get revenge on her captors and used a fallen Paegaas Workshop Spiker to shoot Parabum in the face repeatedly, before she herself was decapitated. Any surviving members of his pack would have been killed by the UNSC reinforcements, which landed on Beta Gabriel soon after and eliminated all of the Jiralhanae survivors.
Parabum kept his face unshaven (akin to the Jiralhanae in Halo 2), as opposed to Ceretus, who shaved his face (akin to the Jiralhanae of Halo 3). In addition, Parabum wore only a few protective shards of armor in key places (also reminiscent of the Jiralhanae in Halo 2), rather than the highly decorative armor of most Chieftains Connor Brien had personally encountered
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