The Wolf King is a figure in the Karaethon Cycle that signals the end of the age.
Spoken of briefly in Knife of Dreams by Banner General Tylee Khirgan, it appears that sections of the Karaethon Cycle speak of a king of wolves, who will lead all wolves into battle on the Last Day at Tarmon Gai'don. It speaks also of the announcement of the final days when the wolf king carries a hammer.
Very few people are known to speak to wolves, the two central to the plot at the moment are Elyas Machera and Perrin Aybara. Perrin, being the one of the two who leads an army and carries a hammer is almost certainly the Wolf King of the prophecies.
The Seanchan noblewoman spoke jokingly of the prophecy when she saw the Wolf Head Banner and Perrin carrying a hammer, as if suggesting that the Last Battle was nigh, though she dismissed this as a bad thought.