Luffy = Cimmerian warrior (as Conan) and Pirate in Barachan islands
Zoro = Hyrkanian swordsman (as Subotai) with ancestors from Khitai
Nami = Vanir thief (as Valeria) who will learn witchcraft
Usopp = Argossean thief
Sanji = Aquilonian (Gunderman) mercenary
Nico Robin = Hyperborean assassin and bounty hunter, learned ancient hyborian chronicles.
Chopper = Deer turned into Beast man by wizards from Nordheim
Vivi = Stygian (high caste) princess covering as Zamoran thief and bounty hunter.
Franky = Kothian gladiator
Brook = Ancient undead wizard and swordsman from the fallen Acheron empire
Jinbe = Spawn of Dagon from Thurian Age
Shanks = Vanir warrior and pirate
Garp = Cimmerian chieftain
Dragon = Cimmerian mercenary
WhiteBeard = Aesir chieftain
BlackBeard = Stygian (low caste) dark wizard and cultist of Set
Imu = Ancient Snake woman from Valusia
Rebecca = Zingaran warrior princess (as Red Sonja)
Gold Roger = Zingaran (Barachean) pirate captain
Ace = Zingaran raised as Cimmerian, joining Aesirs.
Sabo = Aquilonian (Gunderman) raised as Cimmerian
Hancock = Shemitish princess (as Belit queen of the black coast) raised by Picts
Kaido = Turanian warlord
Beast pirates = Turanian and Hyrkanian nomadic hordes
Doflamingo = fallen Zingaran noble
Crocodile = Kothian thief lord and bounty hunter
Ener = Kosalan cult leader of Xotalanca
Kidd = Nemedian warrior
Caribou = Zamoran thief
Oden = Khitan warlord and noble
Gorosei = Snake mens of Valusia
Dorry and Broggy = Frost giants from Nordheim
Arlong = Deep one from the cult of Dagon
Marguerite = Pictish female warrior
Bon Clay = Ophirian court buffoon
Baggy = Aquilonian court buffoon
Cobra = Stygian pharaoh
Trafalgar Law = Aquilonian (Poitanian) warrior and swordsman
Alvida = Zingaran female pirate
Don Krieg = Nemedian warlord

In the Hyborian Age, long before the world was drown into ocean and the rise of the sons of Joyboy. There was a warrior fighting evil gods and wizards.