The following is based on Fallout Tactics and some details might contradict canon.
Bunker Alpha is the main base of operations for the Brotherhood of Steel in the Midwest, located in a pre-War bunker near the former city of Chicago, Illinois, established some time after the Brotherhood airships crashed there. In time, the Brotherhood established a harsh rule over the towns and tribal villages in that area, controlled from Bunker Alpha. General Simon Barnaky was stationed here, before moving to Bunker Beta.
It is here the Warrior began his career in the Brotherhood, and it is from here came the destruction of raiders in the Chicago region.
The bunker was inhabited by many paladins, knights, scribes, and elders. Later, tribals arrived as new initiates. The quarter master of the bunker was Octavius, the recruit master was Yeoman, and medical officer was Celsius,
who later moved to bunker Beta, being replaced by his assistant, Timothy. The initiates Tiduk and his sister Shauri also presented themselves to the Warrior. Pilot Christian could be spotted near the exit. Later, Nanuk, the freed tribal, will appear in the bunker, and a mechanic named Smith will be available to trade.