Iago Mere prattle without practice Is all his s... - WAEC Literature 2017 Question

Iago:    Mere prattle without practice
         Is all his soldiership, But he, Sir had the election;
         And I, of whom his eyes had seen the proof
         At Rhodes, at Cyprus, and on other grounds
         .....must be belee'd and calmed
         By debitor and creditor

(Act 1, Scene One, Lines 23-28)

Sir refers to__________