Who is Rhiotamus?  

and

   Who is Riothamus?

This is very easily professed. Rhiotamus is only a typing mistake. Years ago, I was on the search for a right user name for internet auctioneers. (and which one?) Nothing matched. But because I am a bookworm I always read books. At that time it was "King Arthur" of Geoffrey Ashe.

I had an idea: Riothamus, the celtic prince and military leader. Then I made a typing error and ... I had a new name: Rhiotamus !!!

Since that time the prince walks with me by the internet. In different variants, but always the celtic warlord.