Ratchet: "Did you say something about a curse?"
Wind Turbine Operator: "Well, yes! The curse of the undead! Though, I'm not sure how you can be 'undead' when it just means, you know, alive! Oh, now I just confused m'self!"
—Ratchet and the Wind Turbine Operator, discussing the Curse of Darkwater[src]
The undead pirates were space pirates cursed by their captain, Angstrom Darkwater. When Darkwater's first mate, Romulus Slag, led a mutiny against the captain, any pirates who stayed loyal to Captain Darkwater were killed. Darkwater himself was decapitated by Slag during this massacre. Slag then became the new pirate captain, and left the deceased bodies of Darkwater and his crew at Morrow Caverns, Planet Merdegraw.
Many years later, Captain Slag had his own head removed by Ratchet. Slag's loyal first mate, Rusty Pete, revived Slag's head, and promised his captain a new body. At Morrow Caverns, Pete fulfilled Slag's wish by attaching his head onto Darkwater's body. This also activated the curse, causing Darkwater and his crew to return as undead beings. These undead pirates were now free to roam and raid Merdegraw. It was now up to Ratchet to fight off this army of the living dead.
The undead pirates were a lot like the regular pirates, except that they resembled animated skeletons, and emitted a ghostly green light around them. The undead versions were also much stronger. They would also appear out of nowhere to attack Ratchet.