According to director Taika Waititi, they simply brought more of actor Chris Hemsworth to the role. Here’s what he said:
We actually made Thor closer to Chris in his personality and likeness and who he is. He’s funnier, a lot funnier. A lot more colloquial, because he’s spent time on Earth. Personally, I think he’s the best version of Thor, just quietly, not to take away from the other films, but in order for me to feel comfortable making this film, I wanted to move away from those other films, and make something that was kind of a standalone Thor film, and that you really didn’t need to see the first two to understand this one.
One thing that helped infuse this new personality into Thor: Ragnarok was lots of improvisation. Waititi said about 80 percent of the movie was completely ad-libbed, with the director shouting out ideas from behind the camera.