There's a chance that a few characters from other Fallout games traveled to the Commonwealth for various reasons. Here are the enemies and friends we expect to return in Fallout 4.
If you haven't played Fallout 3 in years, you might not remember Madison Li. Nonetheless, she was there for the beginning and end of the game. Li helps deliver the player when he or she is first born. She's also the one who asks them to risk their lives to fix Project Purity.