He was created as part of an attempt by Caulder to achieve immortality by dowloading his mentality to the clone. He objected to Caulder's experimentation and research. This eventually led to his betrayal of Caulder by allowing Will and Lin into the Great Owl. Caulder foresaw this, ordered Penny to crash the Great Owl with Will and Lin onboard, and then captured and poisoned Cyrus. However, Caulder had the poison kill him slowly, a mistake that allowed Cyrus to live just long enough to talk to Will again and provide him the location of the nest and the cure to the Creeper.
A year later, when Dr. Morris finishes curing the Creeper victims, he and Will talk about Cyrus's unexpected heroism.