Executive Officer
This character is second in command after the ship's Commanding Officer. He/she is responsible for assisting in the command of the ship during the story and overseeing the SIM in the CO's absence. SIM administrative duties may be delegated to the XO by the CO as needs arise. The Executive Officer should be the right hand man to the Commanding Officer and capable of stepping in to run the SIM. The qualities that make a good CO, apply for the this position as well. Executive Officers are selected by the CO of the particular ship.
The XO plays mainly on the bridge, but like the CO, can be moved all throughout the ship and on most of away missions.
Examples from Star Trek are Mr. Spock, Cmdr. Riker, and Cmdr. Chakotay.
