Sentence:  He was in the middle of organizing his massive stash of rare and exquisite bounty, all kept safely in the inventory cache of a <WSD>mule</WSD>, an entirely separate character which he paid a monthly fee to maintain exclusively for that purpose. 
Meaning of the word marked with <WSD> tags:  A MMORPG character, or NPC companion in a tabletop RPG, used mainly to store extra inventory for the owner's primary character.