User blog comment:Skeith9/Heroic Spirits Speculation/@comment-82.141.107.33-20170925103405/@comment-1458758-20170925170109

Well remember before the Grail was corrupted, the heroes summoned were typically "Good" with the exception of Assassin. So likely all of them are culture heroes of one kind or another. Berserker is likely Harold Fairhair, the guy responsible for the first Berserkers in warfare. Since they were supposed to fight either bare or 'bear' skinned depending on your interpretaetion.