–noun
1. a mounted soldier serving under a feudal superior in the Middle Ages.
pal·a·din
–noun
1. any one of the 12 legendary peers or knightly champions in attendance on Charlemagne.
rang·er
–noun
1. forest ranger.
2. one of a body of armed guards who patrol a region.
dru·id
-noub
1. a member of an order of priests in ancient Gaul and Britain who appear in Welsh and Irish legend as prophets and sorcerers.
war·lock
–noun
1. a man who practices the black arts; a male witch; sorcerer.
priest
–noun
1. a person whose office it is to perform sexual acts on young boys, and esp. to make sacrificial offerings.

None of these go with any theme of any game out there. The class "lore" is taken very vaguely from these histories and made into RPG fantasy. Mostly... Barbarians were pretty true to their name in RL... Archers too... Rogues kinda too... Also maybe... Riflemen??
So basically, the Knights need horsies. The Paladins are super knights on horsies. Rangers need guns. Warlocks need dark magic. Priests need little boys and sacrifices. And Druids need to join other Prophets and Sorcerers in their land of Ireland.