User blog comment:Draevan13/Great Elder Scrolls Youtube videos./@comment-1600847-20131119052606/@comment-1600847-20131120050958

It's always a possibility. I'm not saying "it's guaranteed he's only becoming High Kig because he wants power". It's what I believe based on what I see and hear in-game, and that, as a history nerd, I've seen this story play out many times before. But it could be mixture of reasons. It could be none of these reasons. Maybe he's a Thalmor in disguise plotting to overthrow humanity! You never know.

Except that Tullius answers to Mede. If he tried to take the Throne, he'd just be executed. Plus, we see via the few of Elisif and Tullius' interactions with one another that they're always arguing. She wouldn't just submit and do whatever he asked.