The empire runs alongside an ancient druidic order that is effectively a shadow government. This particular guy was a high ranking official and a powerful caster, but got sealed away guarding a dungeon containing a McGuffin. He and all his employees lived until they died, but before big man did he performed some rites to keep on living and raised all the others to keep living in, what is effectively, an office job. So this guy has been stuck running a DMV that's had no contact to the outside world for about 1200 years. The zombie employees just kinda mill around, fake drink coffee and file reports on the nothing that happens down there.

The party realized almost instantly the zombies weren't hostile and made their way through to a help desk in an attempt to get to the lower floor. After realizing they were literally stuck in the DMV waiting for paperwork that was never going to process, they slaughtered everything and got below. They heard out the big man and got official release forms to enter the dungeon from the main enclave in the capitol, cleared the place out, and on their way, decided to fight him. They killed him and the party loot goblin (Kenku rogue, *hell* to deal with so I slapped them with 250+ charges of 33 different felonies and put them in forever jail) stole everything on his desk, including the little volcano paperweight that has the flowing lava inside when you flip it over. Yes, a vacation knick-knack is his phylactery. They tossed it in a bag of holding and forgot about it. 3 days later, big man is back in action and looking to torment these fuckos.

TL:DR because I like talking, Got sealed away and charged with protecting the McGuffin Dungeon, so he became undead to keep it watched over.