Rhombus

Rhombus was the Head Paladin of the Brotherhood of Steel in 2161. He assumed this position when the previous Head Paladin, John Maxson, became the new High Elder after his father was killed by the Vipers. The Paladins, now led by Rhombus, began a full scale campaign against the Vipers, tracking them down and wiping out almost all of their members within the span of a month. He's not one for conversations and if angered him, Rhombus would kick the Vault Dweller out of the Brotherhood of Steel. He promises to train the Vault Dweller once the super mutant threat is removed, we don't know if he ever does.

After the death of John Maxson, Rhombus became the new Brotherhood High Elder. Given that all three previous High Elders and one of the future ones (Jeremy Maxson) were from the Maxson family, Rhombus might also have some ties to this "dynasty", although there is no evidence either way.

Tell Me About
You can ask Rhombus about the following words: Vree, Rhombus, Talus, Elder, Scribes, Knights, Hub, Disks, Army, Boneyard, Paladins, Master, War, Exodus, Strange Army, Merchants, Missing Caravans, Children of the Cathedral, Initiates, Chip.

Alternate history
In one of the endings for the Brotherhood of Steel in Fallout 1, it is said that in the 2180s the Brotherhood, now called the Steel Plague, devastated the newly formed NCR and started a Dark Age that could last a thousand years. This ending is, however, not part of the canon Fallout background. This ending is available only if Rhombus is killed, which means that his survival is crucial for the Fallout world as we see it in Fallout 2. If he survives, a picture of elderly Rhombus is shown for the "good" BoS ending, which means that he most likely became the High Elder after the death of John Maxson, and (presumably) the first High Elder outside the Maxson family.

Rhombus in Fallout Games
Rhombus appeared in the first Fallout game as a Talking Head voiced by Clancy Brown. He was an unlockable playable character in the Fallout: Brotherhood of Steel game.