Alex Sartorius

Dr. Alex Sartorius is an unseen character in Batman: Arkham Knight. He was the skilled biomedical scientist and the co-founder of Stagg Enterprises, who created Cloudburst.

Before Arkham Knight Incident
Alex Sartorius was raised in a Catholic family, but chose science over faith and became an ingenious scientist. Sartorius co-founded the pharmaceutical company Stagg Enterprises with his friend Simon Stagg, who took the business side of things while Alex, not being fond of attention and simply wanting to help people, took the science parts. Despite much of the good the company did, Stagg Enterprises went broke and Simon started making Alex perform illegal human-experiments to create bio-weapons for the government, other countries, and criminals like the Scarecrow. This greatly damaged Alex's psychological state and made him require anxiety medications in order to function.

Eventually, the burden of guilt became too much for Alex and he recorded tapes confessing to Stagg Enterprises' involvement with the Scarecrow. Not long after, Stagg summoned him and accused him of betrayal. Alex was put in one of Stagg Enterprises' own human-experimentation chambers and subjected to doses of fear-toxin which caused him to believe that his body was consumed by fire. What happens to Alex is unknown.

Trivia

 * In the comics, Dr. Alexander Sartorius is actually a supervillain known as Doctor Phosphorus whose body was radiated by a cracked reactor core turning him into a flaming skeletal superhuman with radioactive powers and an inmate of Arkham Asylum.
 * Alex's fear-gas hallucination being him burning up in flames is an allusion to his character's comic-book counterpart.