Overlord Knights
Overlord Knights in the Stellaris encyclopedia: Overlord Knights turn Alloys into Stability and spawn Defense Armies for the Subject, and Unity and Research Points for the Overlord.
Overlord Knights in the game's words
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Overlord Knights turn Alloys into Stability and spawn 
Defense Armies for the Subject, and 
Unity and 
Research Points for the Overlord.
Completing Knightly Quests can further improve their output.
Trained for combat; well educated; virtuous. These knights represent the very best of our society, and they have dedicated their lives to the search for the Toxic God.
Entries that mention Overlord Knights
Source: common/game_concepts (concept_overlord_knight) and localisation/english, Stellaris Cygnus v4.5.2 (9776).