The first two movies in the Thor franchise never touched on why Odin is one of the most powerful beings in the Marvel Cinematic Universe. Of course, we saw him defeat the Frost Giants, but that was just a flashback. In the present time, he hasn't really done much to reveal the extent of his strength, which is a shame. Most recently, though, we learned that he wasn't just Earth’s protector; he kept the entire Universe safe.
Thor: Ragnarok producer Brad Winderbaum said that Odin's power kept chaos at bay. Not only were the fans unaware, he kept it a secret even from those who were closest to him. When Thor started his journey following the events of Age of Ultron, he saw that the universe had changed, but he couldn't figure out why.
When Loki took the throne of Asgard, he also didn't know that the All-Father was actually a protector of the universe. The arrival of Hela - one of the MCU’s biggest threats – took him by surprise. Winderbaum said that Loki was left with just one option: joining Thor's Revengers:
What Thor comes to learn early on is that there’s a lot of terrible things in the cosmos that just shouldn’t be that way. And we learn that Odin was doing far more than it seemed on the surface to keep the universe safe. That there were all these threats that he had quelled or was keeping at bay, using his strength and power to do so, that Loki was completely unaware, unprepared for. He becomes the King of Asgard, everything is great, it’s a good party, but he failed to realize the threats that were just over the horizon, Hela being the biggest and most terrible one of all (IGN).
Of course, there are questions: If Odin was so powerful, how did Loki manage to take his throne? Why didn't Odin see that Thanos was coming or that he posed an even worse threat than Hela (read more about Odin vs. Thanos)? We expect to find out when Thor: Ragnarok is released on November 3, 2017!