Familiar Faces

Familiar Faces is an unmarked quest in Fallout 4.

Detailed walkthrough
Talk to Daisy in Goodneighbor. If you go deep enough into conversation she will tell you that she was alive before the Great War. She will also tell you about another ghoul in Hotel Rexford, who states that he was also around before the Great War.

If you head to Hotel Rexford, and go up the stairs, you will find the Vault Tec rep, who is now a ghoul. When you talk to him he will immediately recognize you. Turns out because his name was not on the list to get into Vault 111 he had to suffer through radiation turning him into a ghoul.

If you keep on talking he will tell you that he is lonely and wishes he had a friend. You can invite him to Sanctuary Hills, to which he will respond by saying "Yes. But promise you will visit!". If you promise him you will visit he cheers up, and heads to Sanctuary.

Companion reactions

 * Curie, Robert Joseph MacCready, Nick Valentine, Codsworth, Piper, and Preston like when the Sole Survivor offers a new home to the Vault-Tec rep.
 * Cait, Danse, and Hancock disapprove of the Sole Survivor offering a new home to the Vault-Tec rep.