Copperhead

Copperhead was the person whom sent Three Dog a weapons cache note, with coordinates to the military weapons cache uncovered in Hamilton's hideaway.

Background
Copperhead's dialogue makes the Good Fight sound like an actual organization. This makes Three Dog's banter less of a motivational speech and more of a recruitment campaign.

Relationships
Copperhead is a member of the Good Fight, and personally knows Three Dog.

Appearances
Copperhead is mentioned only in Fallout 3.