As far as we know, there are no photos of Vikings. It's reasonable for someone to use AI for learning about their appearance. If working as intended, it should be as reliable as reading a long description of Vikings on Wikipedia.
Then specify that in your prompt. "... in the style of ..." or "... in a ... setting".
The point is that those modifications should be reliable, so if you want a viking man/woman or an asian/african/greek viking then adding those modifiers should all just work.
