Sonic the Hedgehog first encountered Cyril during one of his many missions, and the elderly eagle thought himself the last eagle on Mobius to survive Dr. Ivo Robotnik's predations. Too weary to even fly, Cyril had all but given up, but Sonic motivated him to try flapping his wings again. Amazingly, Cyril got the hang of it again, and even found surviving members of his rookery. The discovery rekindled Cyril's spirits, and together withhis flock, he helped Sonic survive one of Robotnik's many attacks. (StH: #12)
Cyril later appeared in Knothole and was training the other Substitute Freedom Fighters when Larry Lynx arrived with dire news about Sally Acorn's Knothole Freedom Fighters. Despite his advanced age, the eagle willingly submitted to Larry's command and followed the others in liberating their trapped friends. As result, he was made an official part of the group. (SLV)
Over a year later, Cyril was present at the wedding of Antoine and Bunnie D'Coolette, and was captured along with the majority of the Kingdom of Knothole's citizens during the Destruction of Knothole and subsequently rescued by Sonic and others. Despite still being fairly spry, his advanced age forced him to retire, and the Substitute Freedom Fighters disbanded at about the same time. (StH: #174, #175, #176, CSE)
Because he had chosen to hide in the mountains instead of resisting Robotnik's advances, Cyril considered himself a coward and was depressed to the point that he contemplated submitting to Roboticization. However, Sonic's arrival and the discovery of survivors from his flock stirred his true, feisty nature, leading him to join up with the Freedom Fighters. Evidently his experience impressed the leadership, as he was briefly assigned to help train most of his future teammates.
Cyril, as an eagle, had the natural ability of flight, though he was a bit rusty when Sonic first met him. He quickly improved and began employing this skill in battle, though he displayed few other skills.