Yesaul
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Yesaul, osaul or osavul (Russian: есау́л, romanized: yesaul, Ukrainian: осаву́л, romanized: osavul) (from Turkic yasaul - chief), is a post and a rank in the Russian and Ukrainian Cossack units.
The first records of the rank imply that it was introduced by Stefan Batory, King of Poland in 1576.