Japanese Translation

What would the Japanese translation of “John’s Champion” be, with “Champion” referring to John’s best competitor? (“John” could be any name, but it must be a proper name, not a title, like “King” or “Lord”.)

Thanks ahead!

John no champion.

Seriously. “no” shows possession in this case, and “champion” is very commonly used and pretty much universally understood in Japanese. The pronunciation is also the same.

If you want a more japanese-looking word, you could also use yushousha (or yushosha if you don’t care about showing that the o is long).