I like Ragnar (quick google), turns out Ragnar is a legendary Norse ruler …
If we look at the names in the desktop Tuesday - Sean, Brom, Nol, Mer. The names have a certain feel to them, I don’t think alliteration fits, I feel it makes it sound a bit cheesy.
Ragnar is a pretty awesome name though, I imagine him being in a band of roving mercenaries hunting goblins and criminals.
For a nickname though, well, call him whatever you want!