I am trying to remember the names of a series of fantasy books?

It was about a guy, an engineer I think, in our world, who was taken by a god into another world. He was given a powerful body and was a master swordsman. The whole society was based on sword fighting. He was supposed to stop a group of people who were terrorizing the rest. He figured out they were using gunpowder and other technologies that the rest didn't have. He had a skinny apprentice. I think his name started with N. The apprentice became a better swordsman than the guy.

Any thoughts? Thanks.