Simon Stagg was the co-founder, alongside his business partner Dr. Alex Sartorius, and CEO of Stagg Enterprises, a pharmaceutical company that was predominately stationed in Central City. While Stagg displayed an ethical image and a company that worked to create vaccines to cure certain ailments and diseases, his true face was one of a deprived sociopath, who used hundreds of volunteer and abducted human test subjects, many of whom horrifically perished during trial periods, including Dr. Sartorius, to further research on biological weapons to be sold to the military, including armed forces that were in conflict with the United States.
Stagg came to Gotham City via his Zeppelin laboratories, and formed an alliance with Dr. Jonathan Crane, better known as The Scarecrow, to perfect his signature Fear Toxin and use it in conjunction with a device called the Cloudburst to create a weapon of terror. After he was driven by the commercial and lucrative opportunity that such a toxin and device would secure him with, Stagg planned to betray Scarecrow and sell the device for his own purposes, a mistake that ruined his career and nearly cost him his life.
At least twenty years prior to the events of Scarecrow's attack on Gotham on Halloween, Simon Stagg and Alex Sartorius made a medical business. However, Stagg took most of the credit for the inventions, including a treatment for Collier's Syndrome and the cure for the Tugela Virus that was actually developed by Sartorius. Despite that, Sartorius was fine with not getting the credit, as he wasn't one to go for the limelight anyways, nor was he about the financials. Sartorius also constantly believed Stagg when he claimed that he'd take care of the budget. However, Stagg may have lied constantly, with Sartorius suspecting that Stagg had lied to him after he discovered that the year after those events' budget had a gaping hole in it.
That ultimately led to Stagg making more unethical decisions, and started with getting weapons contracts for biological weapons. Stagg then proceeded to decide that not even killing them was enough for him, especially when there weren't many legal buyers for the bioweapons or chemical weapons, and proceeded to abduct thousands of people to experiment on them, despite human testing being extremely unethical, not to mention highly illegal and life-threateningly dangerous, with his assuring Sartorius that the people he abducted "won't be missed." It was presumably around that time that Stagg also was rumored to have nearly had one of his former employees, the microbiologist, Robert Kincaid, assassinated due to having knowledge on controversial research, although the rumors were never confirmed, with the only hint at its veracity being him having a bullet from an outdated hunting rifle lodged in his upper arm.
Some time after the events of Arkham City, Bruce Wayne attempted to get funding to help his Gotham Reborn Project from Stagg, but Stagg was more interested in setting his daughter, Sapphire, up on a date with Wayne.
Sometime later, Stagg bought some mud from an antiques dealer that came from Clayface and gave it to the R&D department of Stagg Enterprises to develop weapons. That eventually was supplied to Hush by the Arkham Knight as a mutual desire for revenge against Bruce Wayne.
By the time of the events of Scarecrow's attack, Stagg had started to sell some of his bioweapons to the United States Army, and even more to the groups that the Army was fighting against, which meant that he underwent war crimes and treason, and Sartorius became disgusted enough with his actions that by the time that Stagg enacted the deal with Scarecrow, Sartorius intended to make a recording that exposed his employer.
On September 3rd, Stagg was approached by Scarecrow, who went by the name of Dr. Jonathan Crane. Stagg initially thought that Scarecrow was interested in modifying and selling the fear toxin for a profit, although he eventually came to realize he was still going by Scarecrow, and was both shocked and disgusted that Scarecrow would use a formula that the supervillain had invented to frighten people when he could have used it to cure depression or even turn an entire army on itself. Stagg nonetheless agreed to work on the Cloudburst for Scarecrow, although only so he could modify the fear toxin to make a profit.
A week later, he exposed a test subject named Daniel to fear gas.
A couple of weeks later, on September 20, Stagg had one of his human test subjects exposed to the fear gas, with his begging Stagg to let him out and let him go home in a terrified tone, with Stagg stating the testing had not had as much of a breakthrough as he had hoped. By that point, the Cloudburst itself was operating perfectly, although he did not reveal that to Scarecrow, as he still intended to perfect the fear toxin himself.
A week later, on October 2nd, he then checked up on Daniel, who by that, point had undergone two weeks since his exposure. By that point, although he had mild terror, Daniel was also given permanent brain damage to such an extent that he could no longer speak coherently, let alone beg to go home and be released, with Stagg stating that it wasn't good enough.
Two weeks later, on October 14, Stagg then witnessed a patient named Mr. Huxley being exposed to fear gas. That time, the test was a success, so much of a success in fact, that they actually had to restrain Huxley due to his being in an enraged state, and yelling that he'd kill them all.
At some point, Stagg became privy to Dr. Sartorius' plans to expose him. He then had a militia soldier come to his office under the pretense that Stagg wanted to have a "talk" with his former friend. Stagg then proceeded to make Sartorius a test subject to the fear toxin.
On October 29, Stagg had managed to perfect the fear toxin to such an extent that even equipment that would normally deter toxins such as gas masks and other protective clothing were completely useless against it, due to it readily passing through the skin and eyes. He then decided that, combined with the Cloudburst, the potential was world-changing as well as lucrative. However, he also realized that Scarecrow was unconcerned with a profit and had just wanted to settle a vendetta. Stagg then decided to leave Gotham before Scarecrow returned, and resolved to dissolve their partnership.
Unfortunately for Stagg, Scarecrow had anticipated the depraved businessman's treachery, and via the Arkham Knight's Militia, intercepted his blimps with the Arkham Knight just after they had captured Oracle. Batman then saved Stagg, with him also lying to the Dark Knight about the properties of the Cloudburst and why Scarecrow had wanted him dead. Stagg was then recaptured by the Arkham Knight's Militia on Scarecrow's orders and was taken to the second blimp, with Batman unwillingly allowing them to do so due to a combination of both the fear toxin that he had been exposed to and The Joker's blood in his systems, which caused him to hallucinate the Joker's crowd presence.
However, because of Stagg failing to inform him about the Cloudburst's operational status, Scarecrow was forced to have the device recharged due to Stagg's neglect in keeping it maintained, and had the Arkham Knight's Militia defend the device as well as retrieve power cells to put them in. Stagg tried to escape, but was ultimately recaptured, although not before he left some of his DNA behind, and Batman later used that to reconstruct a handprint that was modeled after Stagg's own to access his files. Batman eventually uncovered the truth behind the Cloudburst.
Meanwhile, Stagg was then thrown into a gas chamber by a Militia Brute, despite him begging that he was so rich that not even Batman could stop them, only to be rebuked for his double-crossing Scarecrow, and also inferring that he'd only be sorry once he's exposed to the gas, and caused him to beg for help knowing full well what the gas's effects entailed. Batman then saved Stagg from the Militia, and then confronted him with the knowledge that he had lied to him about his role with Scarecrow. He then admitted to the truth. However, before Stagg could tell Batman what the Cloudburst could do, the gas activated, and infected him. Batman then resolved to "leave [Stagg] to his nightmares" by grabbing him via the Batclaw and slammed him against the bars.
Stagg eventually regained consciousness, presumably having the toxin leave his system afterward, freed himself from the chamber, and went into hiding. By that time, the Cloudburst had not only been extracted from the blimp, but had been successfully activated as well. In order to ensure that neither Batman nor the Arkham Knight's Militia could find him, Stagg then activated security measures to lock them out. Stagg was subject to a manhunt by the Arkham Knight's Militia, who had been ordered by Scarecrow to find him and then murder him by throwing him out of his blimp. However, Batman, who needed Stagg in order to find out how to destroy the Cloudburst, had managed to get to him first after he defeated the militia.
After he learned of its properties and how to disable it, Batman then retrieved a fuel cell core that was designed specifically for the Cloudburst for use in the Batmobile, and left Stagg inside a cage near some test-subject chimpanzees, much to his horror, as the chimpanzees, which had been test subjects to psychotropic medication, would have most likely mauled him due to not being fed for days. Stagg was presumably busted out by the GCPD from the cell and airlifted, which likewise resulted in his arrest.
When Batman discovered his presence in the GCPD Maximum Security cell, Stagg then commented on how he expected to be rescued rather than be arrested for his crimes, with Batman noting that he was even more deluded than even he imagined, with Stagg noting that he should know. The GCPD also collected enough evidence to Stagg's role in Scarecrow's attack that Aaron Cash, in his recording on Stagg's entry in the GCPD Evidence Room, noted that after that night, the GCPD would be confiscating a lot more from Stagg Enterprises for his role (which strongly implied that his company would face an inquiry and would likely be shut down).
- Dr. Alex Sartorius: Damn it! Sorry! Sorry! Dropped it! Jittery hands. Keep thinking someone's going to barge through the door any moment. The scotch probably didn't help. Sorry! Forgot to introduce myself, didn't I? My name is Alex Sartorius. Dr. Alex Sartorius. And this? Well I suppose this is my confession. Twenty years ago, I went into business with my friend and business partner, Simon Stagg. It feels strange, talking into this thing. I've never been one for the limelight. Never cared for attention. He was the businessman. I was the scientist! Stagg Enterprises was a fine name by me. And we did fine work, too! I want you to remember that, whatever comes out. The cure for the Tugela virus - that was us! The treatment for Collier's Syndrome, that was us too. No, not us. That was me. I never cared about the financials, of course. Never needed to! "Don't you worry, Alex", Simon used to say, and I believed him. Believed him right up to the day he told me there was a big, gaping hole where next year's budget was supposed to be. I wonder now, of course, if he was lying. Can you blame me? If he'd just come out and asked me I'd probably have said no. I'm no bleeding heart but if there'd been no need... Sorry, I'm getting ahead of myself, aren't I? It's these anti-anxiety meds - that rattle your brain. What I'm trying to say is that day, the day we ran out of money. That's when the weapons contracts began.
- Dr. Alex Sartorius: Hello? Yes, yes, hello! I'm in a better mood today. I've discovered a pharmaceutical cure for paranoia, you see. You put the anti-anxiety pills straight into the whisky bottle, and you swirl it around... Now. Where was I? Oh yes! Chemical weapons. Biological weapons. Wonderful things. We went into business to save people. But it turns out that killing them paid better. But not well enough for Simon, though. That greedy, grasping parasite. That bastard! There aren't many buyers for this stuff, you see. Not legal buyers, anyway. So you had to be competitive. But how can you do research, quickly, when human testing is illegal? Not to mention life-threateningly dangerous. Unethical. Unfathomably risky. Well? It's obvious. You do human testing anyway! He never told me where they came from. Just that no one would miss them.
- Dr. Alex Sartorius: You think I want forgiveness? You think this is some desperate mea culpa? I was raised Catholic, but I chose science over faith. This is not about me, this pathetic drunken confession. I struck my bargain, let him threaten me into silence while I worked on my vaccines, my cures. So don't judge me, whoever you are, whichever junior reporter at the Gotham Herald was lucky enough to press the play button on this device! No, this isn't about me. This is about him. He's gotten worse. We're a pharmaceutical company in name alone, these days. It's all weapons, some to the army. Even more to the people the army's fighting. And now Scarecrow's here. I know what they're doing. They're taking my technology, my mass inoculation device, and they're turning it to something twisted. Something wrong. Well I won't let that happen! I won't turn a blind eye anymore! This confession will be my epitaph, the proof that I was not content to weigh the good I've done against the evil done by him anymore. If you're listening to this-
- Militia: Dr. Sartorius? Mr. Stagg would like a word.
When Dr. Crane approached me, I though the man had finally realized the value of his chemical expertise. But no. He's still 'Scarecrow' to the bone. The man invents a formula that could cure depression! Turn an entire army upon itself! And he uses it to... frighten people! Fine, Dr. Crane. I'll keep working on your Cloudburst. But I'll keep working on your toxin as well. I'll show him there's money to be made here. One way or another.
Civilian: Please make it stop!
Stagg: Human testing has not been the breakthrough I hoped for.
Civilian: I wanna go home, I wanna go home...
Stagg: The Cloudburst works perfectly, though I've temporarily obscured that fact from Dr. Crane. I must perfect his formula myself first.
Patient number 4. Two weeks after exposure. How are we today, Daniel? (...) Daniel, would you like to go home? (...) Mild terror. Permanent damage. Not good enough.
Stagg: Now we're getting somewhere! In fact, we've had to restrain the patient. Haven't we, Mr. Huxley?
Civil: I'll kill you! I'll kill you all!
The revised formula works perfectly. It passes through clothing and is readily absorbed through the skin and eyes. Gas masks are useless. The results are horrifying. Combined with the Cloudburst, the potential is world changing. And lucrative. Yet Dr. Crane remains uninterested in commercial opportunities. He intends to squander our work, MY work, on a vendetta! It's time to dissolve our partnership. I should leave Gotham before his return.