The X-Nauts are a secret society of aliens whose main goal is to stop Rolf of obtaining the treasure of Captain Morgan. They were created by the giant floating heads to protect the chest from any danger. It's speculated that one of them is secretly the legendary Captain Morgan.
There was a time when the destruction and chaos caused by Rolf was almost unstoppable until Shrek ended his slaughter separating him in two halfs. Shrek then gave to Captain Morgan the chest where Rolf's second half was locked. Today, they are working with Mario Head to kill Rolf and his mutant animals. They are revealed to be the creators of Hooktail and used her just to destroy the King, though Hooktail killed Yellow Yoshi instead.