Let's just say that Attila is still the man we know in OTL history, but in a different tribe/race.
It is circa 400 AD: God had a bad day,drunk to much and messed some shit up:
Attila the Hun is born Attila the Viking, somewhere along the Norwegian coast.
Attila grows up and (because he is the OTL Attila) knows much about horses, the steppes and the Roman foreign policy. He identifies himself furthermore as a Viking. No one in his homevillage and neither his parents (Hilda and Sigurdr) know what the hell a viking is supposed to be - because it is 420 AD and not 900 AD - and everyone wonders why Attila looks like a foreigner.
His father Sigurds tried to get him interessted in farming and fishing but Attila just keeps talking about horse-archers and how he wants to get the half empire when he marries a Roman princes.
Sigurdr wonders what the hell Attila is smoking.