Carol is a resident of Underworld in Fallout 3. She is one of the few survivors of the Great War, making her over 200 years old. She runs her own hotel in Underworld along side her long-time friend Greta, they have been close friends for over 60 years. She also claims to be Gob's mother, although they're not blood-related, she raised him like a mother. If you blow up Megaton and kill Gob, then tell carol about it, everyone in Underworld will turn hostile towards you.
Carol is willing to share her story about the war if you ask. She remembers looking for safety in a fallout shelter with her dad, close to The Mall, after the Chinese first strike bombed the West Coast. Carol had barely entered the shelter, and was turning back to find her father who had stopped to help another family, when the thermal pulse from a nearby nuclear missile flash-vaporized him. She ran out of the shelter to search for him, but instead only found his shadow permanently burned into a wall. The remaining survivors took her back into the shelter.
After the nuclear barrages ended, Carol ventured out into the Capital Wasteland to seek a place to survive. Much of the city had either been reduced to rubble or was still aflame following the nuclear bombardment, but She was able to find safety in the undamaged Museum of American History. Carol made a home for herself in the Underworld section and has been there ever since.