Standing guard alongside Cabbot, a fellow initiate, Darrel is a Brotherhood member who treats the duty of the Brotherhood and his power armor with religious reverence. The armor is sacred, the enemies are heathens, and the Brotherhood is the righteous force of good. He is a pretty decent fellow otherwise.
If the player accepts the Famous Glow Quest, Darrel can give some information on the quest and even supply anti-radiation drugs (if the player character has 3 Intelligence or less).
Darrel will eventually ignore the player, if they talk to him repeatedly.