So I'm probably not the first person who has thought of this, but I have a new theory about Ulfric Stormcloak. We all know that Ulfric is a devout worshipper of Talos, and at first I thought this was just normal worship of the god of mankind, but then I thought there might be another explanation. I believe that Ulfric was familiar with the Arcturian heresy and enviously revered Tiber Septim for his plot to achieve divinity with the whole rebel/king thing. It is well known that Torygg was a devout worshipper of Talos and a proud Nord and may well have joined Ulfric's rebellion if he was asked to do so, but Ulfric didn't ask him because his true plan was not simple rebellion against the Empire, but to reenact the "rebel against the king to become him thing." Torygg once trusted Ulfric, just as Lorkhan made Akatosh trust him and Wulfharth once trusted Tiber Septim. In other words, I think Ulfric caused the Skyrim Civil War for a power-hungry scheme to achieve divinity.
1. King: Lorkhan/Wulfharth/Torygg
2. Rebel: Akatosh/Tiber Septim/Ulfric
3. Traitor: Magnus/Zurin Arctus/Roggvir?
One large hole in my theory that I can see is that an important detail of the Arcturian heresy is that Wulfharth was a shezarrine and Tiber Septim was a dragonborn, and Ulfric isn't dragonborn and Torygg probably wasn't shezarrine, but Ulfric may have planned some way around this.
There are probably many, many things wrong with my theory as I don't understand a lot of the more complicated lore, but I just thought it was an interesting theory/thought.