After the Apocalypse was triggered, Roy and Walt learned about Sam Winchester's role in starting it. Seeking retribution, they tracked the Winchesters down to their motel and held them at gunpoint. Dean recognized them both despite the masks they wore. Before Sam could explain himself, Walt shot and killed him. He then ordered Roy to kill Dean too. When Roy hesitated to do so, Walt did it himself, but not before Dean warned him he was going to be pissed when he came back. 
In Who We Are, Roy and Walt were among the hunters Sam and Dean called to fight the British Men of Letters. Despite their history, both sides held no grudges against each other and Roy and Walt agreed to join Sam's assault on the British Men of Letters compound.
During the attack, Walt acted as the team's explosives expert, blowing open several doors. Walt was one of only three hunters to survive the battle alongside Sam and Jody Mills, the others, including Roy, had been killed in the firefight. When Sam faced off with Doctor Hess, Walt held a gun on her and followed Sam's lead. After Jody killed Doctor Hess, Walt fled the compound with Sam and Jody as it was destroyed by explosives planted by the hunters.
Walt had a very black and white view of the world when first encountered by the Winchesters in Dark Side of the Moon and believed that Sam had to die for his role in starting the Apocalypse. While Roy was more hesitant to commit murder, Walt had no compunctions against murdering Sam and then Dean out of fear that Dean would come back for revenge.
When Walt returned seven years later in Who We Are, he appeared to have put his old grudges against Sam aside. Walt was willing to follow Sam into battle despite his former hatred for Sam, showing that Walt truly had changed from his previous hatred of Sam.
- They share the same name as the Disney brothers.
- Actor Nels Lennarson also portrayed a bartender in the season 10 episode "About a Boy".
- Walt appears to be an expert in explosives as Sam's assault team defers to him in the matter during their attack on the British Men of Letters compound.
- ↑ Dark Side of the Moon