Caste

The Silurians operated on a racially-based caste system which included scholars and warriors. (COMIC: The Lost Dimension)

Ice Warriors had a feudal-like caste system which included Ice Lords (TV: The Seeds of Death) and an Empress. (TV: Empress of Mars)

Eutermesans were inducted into different castes. Such castes included management, food production and research workshops. (AUDIO: The Creed of the Kromon)

The Inter Minorians were divided into two castes: an upper class and the menial Functionary. (TV: Carnival of Monsters)

When the Twelfth Doctor encountered the Sea Devils beneath Ravenscaur School, he suspected that their more aggressive mindset and superior physiology compared to the other Sea Devils he'd encountered indicated that these creatures were the Sea Devils' warrior caste. (COMIC: Clara Oswald and the School of Death)