The inspiration for Bill Tench on Mindhunter, Robert Ressler interviewed dozens of murderers during his career with the FBI and came up with the very first serial killer profiles.

The chainsaw was invented to more safely perform a brutal surgery known as a symphysiotomy on laboring women, during which the birth canal was widened with a hand-cranked, rotating blade.

When four employees vanished while closing up their restaurant in Speedway, Indiana on November 17, 1978, the police assumed they'd run off with the day's cash — but then they were found murdered.

Just a year after she was born in 1902, Albert Einstein's daughter Lieserl Einstein suddenly vanished from the historical record — and until 1986, no one even knew she existed.

The author of Think and Grow Rich, Napoleon Hill claimed to have interviewed Andrew Carnegie and advised Woodrow Wilson — with zero evidence.

It was once almost universally accepted that Robert Peary was the first man to make it to the North Pole in 1909, but a re-examination of his records in the 1980s cast serious doubt on his claim.

When C.P. Ellis was tasked with working with Ann Atwater to desegregate Durham, North Carolina schools, he was an "Exalted Cyclops" of the KKK. Ten days later, he was a strong supporter of the civil rights movement.

After the Persians invaded her lands around 530 B.C.E., Queen Tomyris vowed to give their king his fill of blood. And she kept that promise.

In 1944, Finnish soldier Aimo Koivunen got separated from his unit and survived for weeks inside the Arctic Circle without food or shelter — fueled by a dose of meth large enough for 30 men.

Meet Annette Kellerman, the early 20th-century pioneer who broke swimming records, dove off 90-foot cliffs, and became the first woman to appear nude in a major motion picture.