You had traveled about for quite some time in the wastes, eventually arriving at Vault 81. After managing to convince the Overseer you're friendly and we're willing to give them some fusion cores to help them out, you were granted access to the vault.

Upon entering the vault you see the rather chubby redhead that is the overseer, Gwen McNamara.

"Greetings wastelander, I'll uh.. take those fusion cores off your hands now."