I was thinking along the lines of "the pharaos' various lovers". The rose which never fades, willingly bound throughout eternity to always be with their king-The sales-pitch practically writes itself
...which they are-the catch is, because of shoddy spells cast by Ermorians who were more con-men than conjurers, they happen to be mindless skeletons.
Ofcourse, there's no reason in the world that there can't be more than one breed of immortal-no doubt in many cases the wizards in question were on the level, native, loyal, and powerful. It's just my conjecture that in a lot of cases the Tomb Kings were duped.
After all, who's going to care in a thousand years whether you replaced the saffron in a spell with tumeric? The guy you're casting it on is gonna be dead, and so are you.
Only he's going to be dead and pissed off about it, and you're going to have 30 more good years on *this* plane, and then go off to some afterlive your victim's never even heard of, where they reward who ever dies rich and clever.