The name reached its all-time peak in 2004 with 14 births ranking #5737. FALLING Recent data shows the name is currently falling.
Rudi is a cheerful continental short form usually linked to Rudolf, so it commonly carries the meaning famous wolf. It feels compact, lively, and friendly.
The name has long existed as a nickname and stand-alone form in German-speaking contexts. Its appeal in English comes from being unusual but still very easy to say.