The antibody cocktail that President Trump took to fight his case of COVID-19 was the brainchild of a pair of billionaire doctors.

Leonard Schleifer and George Yancopoulos, the leaders of the pharmaceutical giant Regeneron, built a multibillion-dollar company with a reputation for producing drugs at a breakneck pace and built fortunes that rival the president's in the process.

Representatives of Schleifer and Yancopoulos at Regeneron did not immediately respond to Business Insider's request for comment on the billionaires' personal histories, net worths, or careers at Regeneron.

Keep reading to learn more about Regeneron billionaires Leonard Schleifer and George Yancopoulos.

Regeneron CEO Leonard Schleifer, 68, is a neurologist by trade.

Schleifer, the son of a sweater manufacturer who worked as a code breaker during World War II, was raised in a home on Queens Boulevard in New York City, just blocks away from his future business partner George Yancopoulos, but the two did not meet until decades later, Forbes reported.

Before founding Regeneron in 1988, Schleifer earned both a medical degree and a Phd from the University of Virginia and was an assistant professor of neurology at Weill Cornell Medical College, per Forbes.

President George Yancopoulos, 61, leads Regeneron's research and development efforts.

The son of Greek immigrants who had been refugees in Turkey, Yancopoulos excelled at science from an early age, Forbes reported. He was the valedictorian of his class at New York's elite Bronx High School of Science and was a semifinalist in a national high-school science competition, The Wall Street Journal reported.

"Who you are is where you come from," Yancopoulos told Westchester Magazine in 2016. "I am a product of my environment who became the obsessive-compulsive science guy."

When Yancopoulos was first approached about Regeneron, he was 28 years old and teaching biology at Columbia University, per Forbes.

Despite his accomplishments, Yancopoulos told Westchester Magazine that when people first meet him they think: "That guy is supposed to be smart? He's an inventor and a scientist?"

Regeneron was initially Schleifer's idea.

Before even meeting his future business partner, Schleifer landed a $1 million venture capital investment from Merrill Lynch to found a pharmaceutical firm after negotiating during a 1988 dinner meeting at a Chinese restaurant in Manhattan's Upper East Side, Forbes reported.

Schleifer proceeded to recruit advisors and a board of directors for his new venture, one of whom introduced him to Yancopoulos, per Forbes.

Regeneron has grown rapidly thanks to its unique development process.

To develop its drugs quickly and at a relatively low cost, Regeneron uses a proprietary process in which they insert human DNA into mice, according to Forbes.

Regeneron has produced six different drugs with this process, including its biggest moneymaker, vision loss treatment Eylea. The company sold $4.6 billion worth of that drug in 2019 alone, Forbes reported.

But before Eylea was released in 2011, a string of Regeneron drugs failed, leading some critics to say that the firm was doomed, CNN reported.

"We were never in this for the quick fix," Schleifer told CNN Business' Matt Egan in 2014. "This isn't the software business where you could write a program, everybody loves it and before you know it, you're on top of the world ... We're doing something that is pretty darn difficult."

Regeneron has also worked on treatments for Ebola and MERS, endeavors that helped prepare the company for its work on the coronavirus, Business Insider's Andrew Dunn reported.

The doctors reportedly have a close partnership.

Schleifer handles the business end of Regeneron's operations, while Yancopoulos heads up the medical research needed to develop the company's products, according to Forbes.

It didn't hurt that Schleifer and Yancopoulos' partnership had parental approval from the get-go. Yancopoulos' father accompanied the future chief researcher to his first meeting with Schleifer at an Italian restaurant in Westchester County, Forbes reported. Yancopoulos joined Regeneron in 1989.

"His father wanted to interview me, rather than me convincing George," Schleifer told Forbes in 2013.

Schleifer also has a relationship with President Trump.

Schleifer knows President Trump "casually," The New York Times reported. They met because Schleifer is a member at the Trump National Golf Club in Westchester County, near Regeneron's headquarters.

The billionaires have also worked together professionally. The CEO met with Trump and his coronavirus task force in early March.

As the COVID-19 pandemic escalated, Regeneron began work on an experimental treatment for the new virus.

With the help of $500 million in federal funding, Regeneron is developing an experimental drug to combat COVID-19 in those that have already been infected using an "antibody cocktail," per The New York Times.

In a press release, Regeneron said that initial results from the clinical trials of the drug, begun in June 2019, showed promising results. While Regeneron's cocktail is widely considered one of the most promising treatments for COVID-19 in the pipeline, it does face stiff competition from a similar drug being developed by Eli Lilly.

Still, neither drug has received authorization for emergency use from the Food and Drug Administration, The Times reported.

President Trump was among the first people to take the experimental treatment.

Schleifer told The New York Times that Trump's doctors contacted Regeneron about the drug after the president tested positive for COVID-19.

Although the drug has yet to be approved by the FDA for use in emergency situations, President Trump was able to gain access to it through a special provision called "compassionate use" that allows patients to take drugs still going through trials when no other treatment is available.

Both Regeneron and the FDA approved the president's request to take the drug, and he was given the higher of the two doses currently being studied. Schleifer told The Times that other COVID-19 patients had been approved to take the drug as well.

"All we can say is that they asked to be able to use it, and we were happy to oblige," Schleifer told The Times Friday. "When it's the president of the United States, of course, that gets — obviously — gets our attention."

Yancopoulos told The New York Times that the president's request left him "conflicted."

"This is certainly putting us in a difficult situation ... We didn't want to decide who gets a limited number of doses," Yancopoulos told The New York Times about the president's request for early access to the drug. "I am obviously conflicted, but I probably know the science and the data as well as anyone in the world."

"If it was me I would take it," Yancopoulos said.

Yancopoulos also told The Times that the company is expecting a wave of new requests for the drug from sick patients following the president's usage of it, but a Regeneron spokesperson said that "our first priority is to maintain a sufficient supply in order to conduct rigorous clinical trials."

Regeneron's success has already made its founders extremely wealthy and their COVID treatment stands to make them even richer.

The news of Regeneron's promising COVID-19 treatment sent its stock price up more than 60% in 2020 so far. Regeneron jumped as much as 9.7% on Monday alone after Trump took its antibody cocktail. The stock's gains have sent the net worths of Regeneron's founders soaring, too. Both of their fortunes largely stem from their stakes in Regeneron.

With an estimated net worth of $1.4 billion, Yancopoulos is the first research chief of a pharmaceutical company to achieve billionaire status, per Forbes. Schleifer has an estimated net worth of $2.5 billion.

Schleifer already lives a life of luxury.

Schleifer spends most of his time in the affluent New York suburb of Chappaqua, but also owns a 15-acre estate in Martha's Vineyard, Curbed reported. The billionaire and his wife, philanthropist Harriet Schleifer, purchased the $24.75 million property, which features a pool, detached guest house, and waterfront views, in the area's most expensive home sale of 2015.

The Schleifers have two sons, Adam and David, per The New York Times. Adam is a former US attorney who helped prosecute the "Varsity Blues" college admissions scandal, The Times reported. Adam Schleifer also used a portion of his father's wealth to fund a bid for a New York congressional seat earlier this year, but lost the Democratic primary amid allegations that he was trying to buy his way into congress.

Yancopoulos, on the other hand, reportedly spends his free time planning pranks and watching 'Gossip Girl' with his kids.

Yancopoulos' other pastimes include taking selfies and starting soup cracker fights with his two children, he told Westchester Magazine in 2016.

He is divorced and lives in Yorktown Heights, New York, per Forbes.

"He has always just been our weird, silly, always-there-for-us dad," Yancopoulos' daughter Nia told Westchester Magazine, even when "he was off curing the world's biggest diseases."