Alex Sartorius (Arkhamverse)

Dr. Alex Sartorius was the co-founder of Stagg Enterprises.

Batman: Arkham Knight
Specific details on his past prior to co-founding Stagg Enterprises were unknown, although he had been brought up in the Roman Catholic Church before he gave up faith for science (hinting at his being a lapsed Catholic), and he had pyrophobia.

Twenty years before the events of Scarecrow's attack on Gotham, he met Simon Stagg, and proceeded to form the pharmaceutical company Stagg Enterprises. However, as he didn't care about the limelight or the financials, he let Stagg name the company after himself as well as let him take credit for various breakthroughs the company made, including a cure for the Tugela virus and a treatment for Collier's Syndrome, that Sartorius was responsible for discovering. He also trusted Stagg with the financials, due to Stagg stating he shouldn't need to worry about them. He continued believing it until the year of Scarecrow's attack, when he learned that the financials for Stagg Enterprises had a huge hole in them, causing him to suspect that Stagg lied to him all this time.

He was then forced to let Stagg develop bioweapons and chemical weapons, which was enough of a problem as there weren't very many legal buyers for them, as well as Stagg deciding to break the law by abducting several thousand humans to act as test subjects for the proposed weapons, despite it being unethical, illegal, and life-threateningly dangerous, with Stagg only assuring him that the abducted people "won't be missed." In addition, he also ended up being forced to let Stagg sell bioweapons and chemical weapons to not only the US Army, but also to its enemies, with the latter party having a far larger percentage. The last straw for him was Stagg accepting a business deal with Scarecrow. Deciding he had enough of his friend's unethical actions, he then proceeded to make a recorded confession, also acting as the first time he ever entered the limelight. During this time, he also was developing some anti-paranoia pills, which he eventually succeeded in creating by mixing anti-anxiety pills with whiskey. He also made clear in his recording that he has no intention to garner any sympathy or redemption for his role in Stagg's actions, and is only intending to expose his former friend.

Unfortunately for him, however, Stagg became privy to Sartorius's actions behind his back, and had a Militia soldier bring him before him under the pretense of wanting to have a "talk" with him. He then proceeded to accuse him of treachery, and then made him a lab rat in the fear toxin as his punishment. As a result, he hallucinated his being consumed by fire.

Trivia

 * Unlike in the comics, Dr. Alex Sartorius does not become Doctor Phosphorous. However, his identity as him is given a subtle nod in the Arkham Knight City Story "Lab Rat", which revealed Sartorius' fate and had him hallucinating that he was constantly on fire due to the effects of the fear toxin he was exposed to by his former friend.