First, it’s a who; not a what.
“Erastil” is a fictional deity, in a fictional pantheon, of the fictional world, “Golarion” in the pen & paper roleplaying game, “Pathfinder”, which itself is an OGL offshoot of an older (arguably better) edition of D&D.
Before you doze off, this is not a brainy, obnoxious guild, so I’ll keep the history lesson brief.
Pathfinder Online will be situated in a region of Golarion known as the “River Kingdoms”. It’ll rely on the established Pathfinder lore, but gameplay will likely not be even remotely close to pen & paper.
Incidentally I just liked the write-up on Erastil (he’s not a d-ck), his worshippers would fit the game’s locale, plus it provides our guild with a tidy, memorable acronym (AoE). :D