WARNING: The following contains for X-Men #21 by Jonathan Hickman, Nick Dragotta, Russell Dauterman, Lucas Werneck, Sara Pichelli, Frank Martin, Matthew Wilson, Sunny Gho, Nolan Woodard & VC's Clayton Cowles, on sale now
The guest list for the X-Men's Hellfire Gala includes numerous notable figures from across the Marvel Universe, both heroic and villainous. There are also major wildcards involved in the event, ranging from heroes like the Fantastic Four to villains like Doctor Doom and mutant-haters Homines Verendi. However, the biggest wild card at the event might be Namor the Sub-Mariner, the King of Atlantis who has become a more complex figure in the Marvel Universe in recent years.
While he was willing to work with the Avengers and the rest of the Marvel heroes during the events of King In Black, he's also repeatedly come to blows with the heroic team recently, even fighting tooth and nail to claim the power of the Phoenix Force from them in the recent "Enter the Phoenix" storyline. In X-Men #21, all of this leads Xavier and Magneto to believe Namor might be a perfect new ally and a member of the Quiet Council before the Atlantean monarch refuses their offer.
Namor's oft-forgotten status as a powerful mutant makes him something of a natural potential ally to Xavier and Magneto, especially since Namor previously served as a member of the X-Men during the period when the team relocated to the West Coast and created Utopia. Finding Namor drinking on the and looking out over the ocean, Xavier and Magneto approach the Atlantean and enjoy a pleasant enough conversation, openly discussing "empire building" and how Krakoa has expanded so quickly. But it turns out there's a major reason they wanted to speak with Namor: namely, they want him to join the Quiet Council.
Since the events of X of Swords, there have been two vacancies on Krakoa's ruling body. Jean Grey and Apocayplse both volunteered to leave their positions; Jean helped fight in the final battle in Otherworld while Apocayplse elected to reunite with his family and return to the realm of Amenth. Their attempts to recruit Cyclops and reinstate Jean failed when the pair instead decided to reform the X-Men, leaving two vital roles on the Council vacant. But Namor is unimpressed with the offer and remarks that he is a "real king" and that at night, he dreams of his dominion over all peoples of the world, including mutants. To Namor, taking a position on the Council and joining them as their "peer" would be something of an insult to the Monarch who stands alone, even from those he once called friends.
Namor leaves the conversation with a suddenness that catches both mutant leaders by surprise, noting that they can return to him again when they have something more to offer him than just a position among their number. But until then, Namor will willingly remain apart from the X-Men and maintain his autonomy as the hostile ruler of the world's oceans. It's not surprising that Xavier and Magneto would approach Namor about the open position, especially with Magneto and Namor even recently working together. Namor's wild position on the global scale -- despite his impressive power and potential -- would make him an ideal ally for Krakoa, especially as other nations and organizations conspire against the mutant nation.
Given their own tenuous connections to the rest of the Marvel heroes, Xavier and Magneto may have seen his own recent spats with the Avengers as reason enough to try and entice Namor to join their side. But it's also unsurprising that Namor would be offended by the offer instead of impressed. Outside of full deference to Namor and his royal claim to the world, there was little chance the mutants could actually gain his full attention.
While Namor might be willing to put up with Krakoa, he's already established himself to be an independent entity and one that's willing to fight against mutants if they come into his domain and make trouble. If anything, the pair have only confirmed his status as a wild card for the X-Men on a global scale, and their efforts to bring him in only set up Namor to continue to fill that role for the forseeable future.