Genetically engineer it to have the "Slave Mentality" from GURPS, like the Truul. (GURPS Aliens, the gengineered slave race).
A close fictional equivalent would be the homo servus mod from Drakon, only without the pheromones.
You have the people who do the cooking, cleaning, laundry, low-level clerical tasks, and picking up the litter in the Evil Empire.
(What? Use *people* for servants? Puh-lease. That's only for *special* occasions. You know, those occasions which to any rational mind would be the absolute last time you'd allow people inside the inner sanctum besides your own utterly controlled slaves.
See? I'm trying to be good and not obey the Evil Overlord list, I really am!)
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