Diaz was a henchman of Carlton Duquesne.
Diaz drove a trailer truck full of illegal weapons from the manufacturing plant to Gotham's docks, when the convoy was attacked by a mysterious vigilante. While his escort driver tangled with the Batwoman, Diaz tried desperately to keep the big rig on the road. Most of the weapons were destroyed, and his escort and his co-driver, whom he had sent to the back to dispose of the nuisance, were themselves disposed of. Diaz tried frantically to get away with his life from the fight, but the Batwoman shot his rear wheels out and caused the truck cab to crash off Gotham bridge. He was rescued by Batman, who shot hooks from the Batwing to prevent the cab from crashing into the streets below.