Adjutant
The Esaul is an Ataman's right hand: messenger, quartermaster, deputy and conscience. When the Ataman gives an order, the Esaul is the one who makes it happen, finds the fuel for it, and explains it to the crews in words they will accept. When the crews turn on their Ataman, they very often elect the Esaul. Every Esaul knows this. So does every Ataman.