Yesaul

Yesaul, osaul or osavul (Russian: есау́л, romanized: yesaul, Ukrainian: осаву́л, romanized: osavul) (from Turkic yasaul - chief), was 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.