Plot Choke: Gimme a Hand?

[Gnorman]

Okay, so I have a campaign developed in brief:

Players find Artifact, Artifact Gets Stolen (By those guys with the brain sucking tentacles),

They go to next major city, Red Dragons are Rampaging (In human Form), because Red Dragon Orb was stolen (By the cuthuloids, the King is part of a mind-eating monster worshiping cult)

After investigation, many artifacts are stolen, they clearly need help from magic sentient sword.

The Sword guides them to the underdark where they meet the Great King from Ages Past, who originally owned the sword, he is encased in crystal

The Sword frees him and he aides them in the foiling of the Guys With Tentacles for Chins' plot. (To summon their god from the chaotic future and with his aid restore themselves to the dominant position.)

The part where they free the king is where I have the problem. He's a Badass. a Machiavellian Balls-to-the-Wall super warrior who conquered the world once before. He's too powerful, but for reasons pertaining to follow up plots I need to introduce him here. What I need is for him to have a role in which he is clearly helping the party, and doing something Vitally Important, but also out of the way of their spotlight. Can you help?

He immediately demands their loyalty and conscripts them as his elite squadron of problem-solvers. He then proceeds to build up his armed forces elsewhere to conquer the world once more. Since the evil tentacled ones are his primary competition, his goal is to stop them. So he sends the PCs to disrupt their ritual while he gathers his batallions. The PCs get to do their own thing, and eventually they might have an army ex machina to get out of a bad spot. Of course, they'll likely have to stop the aspiring Machiavelli at some point, but that's further down the line, eh?