Daniel Kahneman, who won the Nobel Prize for his pioneering theories on behavioral economics, has died. He was 90.

The Israeli-American psychologist died peacefully on Wednesday, according to a release from Princeton University, whose faculty he had joined in 1993. His cause of death was not provided.

Kahneman, who also wrote the best-selling book Thinking, Fast and Slow, helped debunk the notion that people’s behavior is driven by rational decision-making, and instead is often based on instinct.

“Danny was a giant in the field,” Eldar Shafir, a former colleague at Princeton University said in the release. “Many areas in the social sciences simply have not been the same since he arrived on the scene. He will be greatly missed.”

Kahneman was born in Tel Aviv in 1934, but his French parents returned home to Paris when he was three months old.

Six years later, as Kahneman was finishing first grade, the Nazis invaded France, and his family was forced to wear the yellow star that marked Jews for mass deportations to concentration camps.

His father, a research chemist, was taken away but then released and the family escaped to unoccupied France and spent the rest of the war in hiding. His father died in 1944, and 12-year-old Kahneman moved to British-ruled Palestine with his mother two years later, just before the creation of the state of Israel.

Kahneman studied math and psychology at Hebrew University in Jerusalem, and went on to earn a Ph.D. at Berkeley, studying statistics, the psychology of visual perception — why things look the way they do — and how people interact in groups.

Then, at 27, he returned to Hebrew University to teach statistics and psychology and began his famous partnership with Amos Tversky, also a Hebrew University psychology professor.

In 2002, six years after Tversky’s death, Kahneman won the Nobel Prize in Economics for their models of how intuitive reasoning is flawed in predictable ways.

Kahneman integrated insights from psychology into economics, especially concerning human judgment and decision-making under uncertainty, the Royal Swedish Academy of Sciences said in its citation at the time.

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