Before 2161, he became the new head paladin when the previous one, John Maxson, became the new high elder after his father is killed by the Vipers. The paladins, now led by Rhombus, begin a full-scale campaign against the Vipers, tracking them down and wiping out almost all of their members within the span of a month.
Gruff, stern and stoic, he does not tolerate nonsense. He is not one for conversations and if upset, will kick the Vault Dweller out of the Brotherhood of Steel. He promises to train the Vault Dweller once the super mutant threat is removed. After the death of John Maxson, Rhombus becomes the new high elder.
Before 2208, Rhombus created a splinter faction of the Brotherhood of Steel, despite some criticism from the elder council because of the former expedition grown by similar ambitions (to track down and assess the extent of the remaining super mutant threat) and the ensuing incident that divided the Brotherhood. He then starts a crusade against the largest faction of super mutants currently existing in the west, the Attis Army.
With some scribes and paladins, he mounted a new expedition which was later named the "Texas Expedition" and began tracking Attis' Army. They followed the army's trail to Texas and there, he discovered the vault prototype, an abandoned vault prototype dedicated to the Secret Vault project and installed themselves as the main base of the Brotherhood of Steel in Texas.
In 2208, Jane, the raider matron and their contact in the town of Carbon, reported movement of super mutants, and therefore Rhombus decided to go to Carbon with a group of paladins. Her information indicated their next destination, the ghoul city of Los. Here, Rhombus ends up being alone, captured, with all his comrades being killed in a bloody battle with super mutants and a local ghoul cult known as the Church of the Lost, but he managed to steal a keycard of the Secret Vault, the final destination of the Attis army and hid it under a truck. Rhombus is tortured by the cult leader, Blake, but later liberated by the Initiate. Afterward, Rhombus assisted the Initiate in getting to the truck where he had hidden the keycard. Once at the destination however, he is blown up by a ghoul suicide bomber.
Unable to continue fighting, he gives the Initiate the keycard and entrusts him with the task of stopping Attis' army and finding the Secret Vault entrance. Rhombus is left sitting near the truck, wounded. However, if the Initiate returns to the place later, Rhombus is nowhere to be seen. His fate is unknown.
"You - you're the only one?!? Those idiots on the Brotherhood council! I warned them that this region contained significant activity! And they sent a - a... You're not even a full paladin, are you? How preposterous!"
"I have fought the mutants all my life, but you may be too young to recall their savagery... They threaten all life because they wish to become the dominant species on earth, crushing the world in their grasp."