Xad has been known as a Scientist, He now works as an irken medic on The Massive. We cannot really see into his past, Except for the fact he has a fondness for Creation. His Wits are only matched by his confidence in the irken empire. However, Despite Xad's Loyalty to the irken empire he despises the current tallest leading over the empire. Beliving that they abuse their power for a main reason of Making Zim's mission impossible.
"My Tallest, I request a mission to assist And other irlens on their conquests. Clearly some are unable to pull them off themselves" - Xad's Attempt to find a better mission.
All of Xad's Medical Supplies Come From his PAK, Supplies of which resemble human medical devices, Simply "fit" for an irken to handle. He wears a metalic Mask So germs can't be breathed in, And an optical assist device scanning in Infared, X-Ray, And Ultrasonic Waves to help with diagnosis. Attached to this device a communication antenna is used to keep in contact with other medics.
Xad rather work in a controlled setting (ie Hospitals, Or offices), However he will never turn down a call for help. However.. He may get a tad sarcastic when annoyed...