Leaked information about Fallout 4 suggests that the game will take place in the Commonwealth, the post-apocalyptic remains of the state of Massachusetts. It's a brand-new location but there may be a few familiar faces there.
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.
Madison Li"The plan was to build a facility that could purify all the water in the Tidal Basin at once. No radiation, no muck, just clear water."
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.
Project Purity, the pet project of Li and the player's father James, was intended to purify the water of the Capitol Wasteland. Players could make the machine work as intended or modify it to poison all humans exposed to radiation along with ghouls or mutants.
Regardless of the player's decision, Li has left the Capital Wasteland by the time of epilogue DLC Broken Steel. Supposedly she headed north to the Commonwealth.
Li could fit into Fallout 4 in a significant way. Maybe she's intent on launching another Project Purity to clean up the water of the Commonwealth region. Or perhaps she has some other plan to decontaminate the wasteland. Either way, she might seek out the powerful scientific organization known as the Institute to assist her in these plans.