Officer

A key, critical, vital and essential military figure and overall commander in whatever battle they're sent into, he/she plays an important role in your armies (military), cities (territories), supplies (lines of supply), battles and technologies or sciences. Officers can reduce the training time for your troops, reduce research times, increase your supplies output and increase attack powers of your troops during battles.

Loyalty
Loyalty can be gained by awarding gold or jewlery to the officer in question. Loyalty can also decrease if you suffered several (severe) defeats or sending a officer to many battles and give no reward. Loyalty which reaches 90 or higher will usually stay that way.

Mayorship (Governance Of A City)
Officers can be awarded the position of mayor in whichever city their stationed in and lower training times, research times,and increase your troops' attack powers on the battlefield. Officers who are mayors or commanders which attack regularly gain experience points which levels up officers which then gives potential points which you can spend to increase your officer's effectiveness on decreasing the training time of your units or reduce your research time.