In the season 6 trailer Bran Stark is seen with what appears to be the White Walker leader. While I believe this is a dream I think the White Walker King is looking for Bran. But why would the White Walker King want to find Bran you might ask. It’s simple Near the end of season 5 during the White Walkers siege on the Wildling camp there was 4 horseman ominously watching the battle from the cliffs overlooking the camp. At some point, one of these horsemen joined the battle and was killed by Jon Snow. Because he died they are probably looking for someone to take his place. I think The White Walker King wants Bran to take his place making Bran one of the four horsemen. Brans ability to warg may transfer when he turns into a white walker giving him the ability to control the living and the dead. It only makes sense that the white walkers find a new horseman because George RR Martin is clearly alluding to the four horsemen of the apocalypse and three just doesn’t cut it.