I should start this off by stating for the record that I have never read the Keyes novels. However, I recall reading somewhere on this forum that Titus Mede I rose to the throne of Cyrodiil in part due to the machinations of some Daedric Prince or another. I do not remember which Prince it was (though my gut tells me Clavicus Vile), and I would be very grateful if someone could not only remind me of the name, but explain the plot as a whole in more detail. How did Mede become Emperor?

I think the theory was that Titus Mede II was backed by Boethiah due to rumors that he wielded Goldbrand at the Battle of the Red Ring.

But I might be mistaken.

It was said in the Great War that he was even placating the Altmeri forces into thinking he was preparing to surrender prior to him starting the counter-attack. If I'm not mistaken, the Prince of Plots digs that kind of thing.

Mede was rumored to wield Goldbrand, and some say that the Thalmor general who was hung from White Gold was spirited away by daedra in what might have been a "deal with the devil." You may have seen me or someone else refer to the machinations of Clavicus Vile. That wasn't Mede's doing, it was Minister Hierem who was the second most powerful figure in the empire and basically paved the way for Mede I in the IC by convincing the Elder Council to embrace him as a conquering hero. They wanted another Nibenean like Thules the Gibbering who could be easily controlled. Mede was watching Hierem as a general precaution, and through his agent started to become suspicious that he was up to no good and attempting to subvert him, but Mede didn't have the political clout to confront him openly.

Big spoilers for the novels and someone correct me if I'm getting details garbled:

Hierem was engineering a takeover of White Gold Tower to make it a landing pad for the floating city of Umbriel, which was a piece of Clavicus Vile's realm that broke off from Oblivion. The Dunmer Sul and Vuhon were blasted into Vile's realm in the destruction of the Ingenium, a device created to hold up the Ministry of Truth after the Tribunal's disappearance. The Ingenium used a portal to Clavicus Vile's realm as part of its power source. Vuhon made a pact with Clavicus Vile to create a new ingenium that would allow him to escape Oblivion- this was Umbriel.

Mede I and his son Attrebus were instrumental in stopping this plot, so he had nothing to do with Clavicus Vile. However in the course of events, Attrebus did wield Umbra* briefly, and may have been changed or ensnared somehow- I really can't speculate on that. *Not just Umbra but a supercharged Umbra which had stolen some of Vile's power.

Thank you. So the plot was going on behind Mede's back, but was supposed to involve him in a peripheral way, and instead of sitting back and letting it happen, Mede and his son stopped it. Is that right?

Ah yes, m'lad, don't buy the rot behind the Thousand-Shields-of-The-West. That yarn's damp floss, har har.

The ha'drake hagiographies the churn out in The City brush in old Titus Mede I a Barbarian Warrior-King of old. Ho ho, what tosh. The moth-logs, sealed now though (little wonder), don't lie: Vespasian Mede (with an accent on the second e) was an old Merchant-Baron, with major shares in Vanech and a Senior Councilorship. He had sons, too. The oldest was a boy was called Titus, and he went to all the finest lyceums and academies.

He also got his damn body deep in with a coven of Tumult-talkers in the Valus uplands. Devotees of the Hell-Prince Boethia.

It suited his ambitions, and the price, he felt, was fair.

Take up the Gold Brand of the foul spirit and run it through his papa's belly.

Then when he had succeded to daddy's place at the Great Table, it was ever so simple to blame the devil deed on his enemies in the Optimate-faction of The Council. That turned a religious fervor in the plebs, and when the commons go, so goes the country. Riots cut through the streets and Chancellor Catafalquo struggled to keep order, giving Mede ample time to smuggle foreign 'Adventurers' into the Center. Then in a fortnight, when his foes were desperate for relief, Mede offered terms: shuffle on out, or the mercenaries surrounding the chamber will shuffle you loose this mortal coil.

One wonders why the bugger wouldn't claim the Septim cognomena. He had all the right venom for it.

Mostly his son and a somewhat rogue Penitus Oculatus agent, and at first behind Mede I's back. Mede I didn't take any real action until Umbriel was headed towards Cyrodiil with undead armies, and by then it was pretty much too late. He's presented fairly sympathetically but with a fatal flaw of being overcautious. As one of the characters says, he doesn't move until he knows where everyone is on the field.