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Fantastic Caste System is the one you want for the general situation
For the sub-components you have:
- Master Race: the leader species
- Slave Race: the grunts and cannon fodder on the bottom of the heirarchy.
- Servant Race: species that perform labor or similar supporting roles, often engineered or modified for this role.
- Henchmen Race: species that serve as soldiers or bodyguards, again often created or altered to fill the role
- Sympathetic Sentient Weapon: often enters when the above were enslaved or otherwise forced into their role
- Planet of Hats: for when each species is defined primarily by some trait or set of traits- the Alicians are all expert engineers, the Bobinites all excel at marksmanship, etc.
- See also Humans Are Indexed for the various hats the master race might want humans for.
Hive Caste System kicks in for the most extreme examples even when they aren't originally same species, so long as they ultimately function as a hive at the time we encounter them. The orks from Warhammer 40k are a good example- orks themselves have numerous caste variantsnote , but any decent ork tribe that sprouts up (literally, they're fungus-based organisms with functional Genetic Memory) is usually accompanied by the Gretchin, Snotlings, and Squigs: separate species with similar biology that play supporting roles in ork society, performing vital tasks such as farming, maintenance, and holding the orks beer while they try to shoot that fly with a rocket launcher.
Edited by Scorpion451
thanks
A specific sci-fi variant of The Empire, consisting of many alien species that each perform a specific function, altered using genetic engineering in order to make them better at their given task. The whole thing is run by a species of physically weak aliens, (who have some other, unorthodox powers in order to make up for their frailty.) who are set above the other species in the empire via a Fantastic Caste System. Usually, this empire would really like to make humanity into one of its slave races, causing the primary conflict of the setting. Especially common in videogames, as it provides an easy in-story explanation for the various types of Mooks - each enemy type represents a different species conquered by the empire.
Examples
- The Dominion from Star Trek
- The Combine from Half Life
- The unnamed alien empire from XCOM
Also, the Covenant from Halo is a borderline example - They check most of the boxes, but they rarely use genetic engineering, and they almost have a second "leader" species in the form of the Sangheili/Elites.