Personality is a slippery and evolving concept that researchers have been trying to put their finger on for decades.The Myers-Briggs Type Indicator (MBTI®) is the original personality assessment tool that changed the game. It was created by a mother-daughter duo with no official training in psychology. And yet it’s used frequently by Fortune 500 companies and the military, as Merve Emre, author of The Personality Brokers: The Strange History of Myers-Briggs And the Birth of Personality Testing , points out in her book. One of the founders, Katherine Cook Briggs, crafted the test after taking an interest in famed psychologist Carl Jung’s theories. “She first concluded that mankind could be divided into four mutually exclusive categories of people: meditative, critical, sociable, and spontaneous,” Emre writes. From there, the test developed and became the dictating force it is today about whether a person is introverted or extraverted, intuitive or sensing, feeling or thinking, perceiving or judging. FiveThirtyEight wrote about the Big Five personality test early this year, which aimed to usurp the MBTI . But theMyers-Briggs letters have staying power.