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 will tolerate no nonsense. He is not one for conversations and if angered, Rhombus 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 "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 key card 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. After, Rhombus assisted the Initiate to the truck where he had hidden the key card. Once in destination however, he is blown up by a ghoul suicide bomber.
Unable to continue fighting, he gives the Initiate the key card 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 Chosen One returns to the place later, Rhombus is nowhere to be seen. His fate is unknown, but he probably escaped Los and returned to the Vault Prototype to send reinforcements, but Los was destroyed by the Initiate when he arrived at destination. The Attis army destroyed, the Texas expedition was finished and he probably returned with the other members of the Brotherhood of Steel to Lost Hills. It is unknown what became of the Initiate and if Rhombus and the Initiate met again after the destruction of the Secret Vault and Los.
"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."
"When I was younger... I would have laughed at a wound like this! Looks like you've finished that abomination Blake... but your work isn't done yet."
"This is no longer my fight, soldier. Here, take my Brotherhood insignia. A sign of my trust... that you will do what must be done..."
"I will be all right, initiate, but you must go now. Find the vault, defeat the mutants... or we face the end of all life... as we know it..."