Originally a doctor, Sharaz Jek gave up the medical profession when he discovered android engineering. This soon became his passion, and being as brilliant as he was, he excelled in it. But his success was to be short-lived - Jek eventually paired up with a man named Morgus, creating a workforce to collect and refine spectrox, an elixir of life only to be found on Androzani Minor. As raw spectrox is toxic to humans, Jek's androids were vital to the process. But Jek's choice of partners was an unwise one, and Morgus soon began plotting to get rid of him so that he could have all the profits to himself. He equipped Jek with faulty detection equipment, and hence Jek was taken by surprise when a mud burst flooded the caverns while he was in them. He was nearly scalded to death, but managed to drag himself to safety in a baking chamber - but the damage was done, and he was horribly disfigured.
Jek retreated into the caves, living only in the company of his androids, who did not care how he looked. This was extremely difficult for Jek, who craved not only the company of intellectual equals, but especially beauty. He became consumed with anger and the desire for revenge, and dreamed of killing his enemy Morgus. In the meantime, he established a monopoly on the spectrox supplies, maintaining his power with an army of killer androids that kept anyone from getting too close.
Jek's years of living with only androids and revenge for company have left him utterly mad, according to Peri, and a raving egoist, according to the Doctor. While these may be subject to debate, the one thing that is certain about Jek is that he has an extremely quick, explosive temper. The slightest thing is liable to set him off into a rage or tantrum. Once handsome, Jek is also extremely sensitive about his appearance, and keeps himself constantly covered in a black suit and tight full-head mask. He is extremely fond of Peri, and wishes to keep her with him forever, but is crushed by her revulsion of him.
