(Covers information from the D.C. comics)
Dr. Callos was the head of research for a secret Umbrella Corporation lab located outside of the Nevada town of Saguaro Wells. He was behind a project to spread the G-Virus through a race of bat-human hybrids.
"Thanks to Umbrella, those fools who denied me funding for my dream will soon be drowning in their own blood."
Little is known regarding Callos' life and career, though it is known he had expressed interest in virus-induced "transmutation". Denied funding from the "fools" opposed to his project, he turned to the Umbrella Corporation in hopes of using the completed experiments to kill his initial opponents.
Researching in an Umbrella complex in the Saguaro Desert in Nevada, Callos began using human test subjects in experiments, mixing their DNA with bats, which he would control with ultra-sonic devices. He intended to use these bats to abduct nine people from Saguaro Wells to be used as the next batch of transmutants. After they were successfully fought off when attacking their ninth attempted abducted, Callos expressed concern the first batch wasn't aggressive enough and would require vampire bats to be used as the second batch instead.
The bats returned the next night empty handed and with one of them injured. Callos reacted by setting the bats on Dr. Vedley, one of his underlings he blamed on the bats' poor performances. Giving up on obtaining a ninth in Saguaro Wells, Callos prepared the eight abductees for transmutation while having the bats fly out for a ninth elsewhere in Elko. Returning with a ninth victim within a few hours, Callos sent the bats away to operate in privacy.
Soon after, agent Leon Kennedy was captured entering the compound. After a brief interrogation, Leon kicked the controls, sending the bats back to the compound. Callos decided he should be killed by them. Unfortunately for him, Leon had a sonar device on him which damaged the controls. No longer manipulated by Callos, the bats quickly turned on him.