I think I have a fan theorie.
Maybe Aerys Targaryen is a White Walker.
One white walker has the same hairstyle as Aerys (and beard and haircolor and face...) - he looks exactly the same.
Also in Season 6 episode 6 we see that Bran has a vision from Aerys where he says: Burn them all. One second later we see the white walkers in the vision, than again Aerys, the white walkers, Aerys and the white walkers.
What does it mean?