Board Thread:Questions and Answers/@comment-29732690-20161105121810/@comment-25942629-20161107185406

The spoiler/fan/unofficial translations are working with a foreign name that was written in Katakana and then translating it back, which is pretty difficult to do. Using the Katakana, they are mostly working with the basic sounds of the name, and then they have to guess what name it's supposed to be. The official translations can contact the people in charge of the Japanese series and get a more accurate translation based on Kagami-sensei's intentions.

Although either name would suit him, but Rigr is his name.

Frankly, I'm happy to see Kagami-sensei putting so much thought into naming characters. Horn's name is just goofy, and he really went wild with names in The Legend of the Legendary Heroes. He even had a character named "Milk."