Who is Finn?

As said, all Stormtroopers are taken from their families from the first moment they are born. In this case, given the supposition that Finn is special, who was his family?

The oldest rumor says that he is the son of Lando Calrissian. The newest one says that he is in some way connected to Mace Windu. Others say that any of these two possibilities would make the galaxy even smaller, since this would be another (rather unneeded) connection – Kylo is definitely a Skywalker, while Rey may also have a famous parent.

Why is Finn so special, after all?