The Long Night is slowly coming toward Westeros, and with it comes the dead. While the royal families engage in political wars with one another, there’s an even greater war that will soon be the focus of HBO’s “Game of Thrones.” Expect bigger things from the White Walkers in Season 6 after they made it known that were a force to be reckoned with last season.

The White Walkers have been in the background since “Game of Thrones” started, and not much has really been revealed about the undead creatures. Each season has contained at least one moment that sheds light on who they are, but they are still basically a mystery.

There’s a reason the pilot episode started with a White Walker before introducing viewers to the Lannisters, Starks and Baratheons. The Great War will eventually become the main focus of the show and everyone will have to come together to stop the dead from taking over everything. Here’s what we know about the White Walkers so far:

The army of the dead is led by a ruler known as the Night’s King, who we will likely get to know more about on the show soon. In the George R.R. Martin's “Song of Ice and Fire” book series, the Night’s King is rumored to be a former Lord Commander of the Night’s Watch, who was fearless. He was believed to be active thousands of years ago, when the White Walkers roamed the land during the last Long Night.

The show has revealed that there are a few ways for the White Walkers to be killed. They need to be burned, stabbed with dragon glass or cut into pieces with a sword made from Valyrian steel. Jon Snow (Kit Harington) and Samwell Tarly (John Bradley) have been the only two members of the Night’s Watch to kill a White Walker.

White Walkers The Night’s King marches towards the Wall with his army of the dead on “Game of Thrones” Season 6. Photo: HBO

There is also a difference between White Walkers like the Night’s King and wights. White Walkers are creatures like the Night’s King and his other commanding officers. Wights are dead bodies they bring back to life to serve their every command. The White Walkers also have the ability to use babies to create White Walkers, which was shown in a creepy scene in Season 4 where viewers learned what Crastor was doing with his daughter’s sons.

The last time we saw the White Walkers was during the Battle of Hardhome in episode 8 of Season 4. Jon Snow had showed up there to try and unite the Night’s Watch with the Wildlings, but his plan was interrupted when the White Walkers showed up. The army of the dead slaughtered hundreds of people and the Night’s King made the dead Wildings wights and made his army even larger. All Snow could do was look on in horror and wonder if there’s anything that can be done to stop the White Walkers. He knows they’ll be at the Wall soon enough.

When Season 6 premieres, Bran (Isaac Hempstead-Wright) will return to the show and he is going to play a big role in the war to come with the White Walkers. In an interview with TV Guide, Wright said Bran’s ability to see past, present and future events could be a big asset in the impending war.

“I think we can all tell things are going to kick off soon enough [with the White Walkers]. Bran’s power is one of the things that could be a real game-changer in one of those wars that are yet to come,” Wright dished.

“Game of Thrones” Season 6 premieres Sunday, April 24, on HBO at 9 p.m. EDT.