Brotherhood of Steel soldiers are members of the Brotherhood of Steel living in the Commonwealth in 2287. They begin appearing in the game after the Sole Survivor triggers the arrival of the Prydwen by exiting Fort Hagen by the elevator leading to the roof.
Brotherhood soldiers are responsible for collecting technology across the Commonwealth and enforcing the will of the Brotherhood. Soldiers who display exceptional loyalty and valor are promoted up the ranks, gaining more formidable gear along the way.
The Brotherhood's soldiers come from various backgrounds, uniting under one flag. Their ranks are (from lowest to highest): initiate, aspirant, knight, knight sergeant, knight captain, knight commander, paladin, paladin commander, and star paladin.
Initiates are commonly found at low levels when traversing the Commonwealth, and when the player character reaches higher levels, aspirants begin to take their place as the "low level." Brotherhood ground soldier.
Knight sergeants slowly start to replace knights in Brotherhood of Steel areas, such as checkpoints, guarding the Prydwen, Waypoint Echo, etc. With the exception of Gavil during the quest Ad Victoriam, They do not have the appropriate paint for their T-60 power armor, instead having common knight paint.
One of the strongest Brotherhood NPCs in the game, at early levels, they will often be found guarding the tarmac surrounding Liberty Prime in a full set of sturdy combat armor of the Brotherhood variant.
A rare and extremely deadly paladin breed, even without power armor they have deadly weaponry at their disposal, and may have several pulse or plasma grenades to disable power armor or quickly kill enemies.
↑Fallout 4 Vault Dweller's Survival Guide: "Soldiers are responsible for gathering technology and enforcing the will of the Brotherhood. Individuals who display exceptional loyalty and valor are promoted up the ranks, gaining more formidable gear along the way."
↑Kal-El Bogdanove on Twitter: "I know I haven't found 'em yet. 😎 But I've heard some of my frequently spoken direction made it into pilot chatter on Prydwen."