Dan Cassidy was a special effects wizard and stuntman who was hired by his friend, film director Marla Bloom, to create and play the title character in the Verner Bros. monster movie Blue Devil. Cassidy's specialty was somewhat unusual - rather than create optical effects that would later be applied in post-production, Cassidy specialized in "in camera" mechanical and cybernetic effects. To that end, Cassidy created a full-body costume for Blue Devil, complete with a powered exoskeleton and built-in pyrotechnic devices. Cassidy also created a rocket-powered prop trident which was, among other things, capable of flying.
During location filming on the mysterious Ile Du Diable, Wayne Tarrant, the "hero" of the film, and his co-star Sharon Scott, accidentally freed a demon named Nebiros. Though Cassidy faced incredible odds and a near-death experience, he was able to effectively use the devices built into his costume to drive the demon back to its home dimension. Unfortunately, he was blasted with demonic energy in the process. After the fight, Cassidy found that the blast had permanently grafted the Blue Devil costume to his body. Cassidy, a devout Irish Catholic, was stuck in the "skin" of an unholy Blue Devil.
