The most commonly mentioned name in this context is Nicola Tesla, he is even featured as such in some fiction (e.g. Tomorrowland). He was brilliant, eccentric, kept to himself, and had some wacky ideas, especially later in life, including persistent search for the ether, see Was Nikola Tesla right about his ether theory? Conspiracy theories around his late life and work were fueled by FBI seizing his belongings when he died. However, and this is were real life diverges from fiction, if the "mad" scientist is supposed to be successful in his "mad" activities, it is not how it worked out with Tesla. He was most successful, indeed brilliant, in his less "mad" early years. Hartsfield gives an interesting take titled Mad Scientists of the Modern Age: Nikola Tesla:
"Edison's light bulb is trumpeted as the signal achievement beginning the electrical era. However, it was Tesla who devised most of the alternating current (AC) electrical systems that the world's power grids are modeled upon. He single-handedly patented AC electrical generators, transformers, power lines, and motors. The electrical system formed by these devices proved so much superior to Edison's direct current (DC) electrical system that it was adopted universally across the globe... Tesla was in many ways the opposite of Thomas Edison. Edison was never known as a brilliant man, but as a methodical, determined one. "Genius is 99 percent perspiration and one percent inspiration," he once said. Tesla was a nearly unparalleled genius, but lacked the business intuition and common sense of Edison. Edison died rich and one of most famous men in the world, while Tesla died penniless and alone, feeding pigeons.
[...] After years of wildly successful invention, Tesla began to lose his way, making grandiose, eccentric and sometimes completely impossible claims. He fervently spoke of building a "teleforce weapon" capable of melting steel wirelessly from 200 miles away. Upon his death, a box supposedly containing a death ray part was found to contain only a basic piece of old equipment. Tesla believed that he could create a camera to project a brain's thoughts onto a wall. He built a 187 foot-tall tower to try to wirelessly convey electric power across the planet, using the earth itself as an enormous electrical conductor. He wanted to harness the entire sphere of the Earth as a power line! Upon picking up odd signals at one of his labs, Tesla believed that they could have been sent from Mars by using that planet similarly as a conductor.
Celibate his entire life, Tesla became lonely and slightly paranoid in his elder years. He claimed to keep his ideas inside of his brain to keep them from being stolen. He was suspicious of twentieth century physics, as explained by Einstein and others... An entire conspiracy theory movement has formed around Tesla's "hidden" or "suppressed" inventions and ideas. The United States government also unwittingly contributed to Tesla's legacy of mad genius. Shortly after his death in 1943, the FBI seized all of his belongings."
Real Clear Science has a whole series on Mad Scientists of the Modern Age, they name Vladimir Demikhov (experimental surgeon known for intrathoracic transplantation), Jack Parsons (jet and rocket propulsion whiz), Lynn Margulis (the founder of endosymbiotic theory), Barry Marshall (discovered the cause of ulcers), and Josef Mengele (Nazi death doctor). On the general correlation between brilliance and "madness" see Why Are Genius and Madness Connected? on Live Science:
"Kay Redfield Jamison, a clinical psychologist and professor at Johns Hopkins University School of Medicine, said the findings of some 20 or 30 scientific studies endorse the notion of the "tortured genius." Of the many varieties of psychosis, creativity appears to be most strongly linked to mood disorders, and especially bipolar disorder, which Jamison suffers from herself. For example, one study tested the intelligence of 700,000 Swedish 16-year-olds and then followed up a decade later to learn which of them had developed mental illnesses. The startling results were published in 2010. "They found that people who excelled when they were 16 years old were four times as likely to go on to develop bipolar disorder... "People with bipolar tend to be creative when they're coming out of deep depression," Fallon said. When a bipolar patient's mood improves, his brain activity shifts, too: activity dies down in the lower part of a brain region called the frontal lobe, and flares up in a higher part of that lobe. Amazingly, the very same shift happens when people have bouts of creativity. "There [is] this nexus between these circuits that have to do with bipolar and creativity"".
