The History of Personality Tests: From Ancient Astrology to Modern Memes

You Have Already Taken 500 Personality Tests This Year

Be honest. You know your Myers-Briggs type, your Enneagram number, your attachment style, your Hogwarts house, and which type of bread you are. You have shared at least one quiz result on your Instagram story this month. You have, at some point, introduced yourself at a party by saying “I’m such an ENFP.”

You are not alone. And this is not new.

Humanity has been sorting itself into boxes for over two thousand years. The history of personality tests is really the history of that impulse — bodily fluids, inkblots, multiple-choice forms, ten-question quizzes on your phone — different tools, same underlying itch: Who am I, really? And can someone please just tell me?

TL;DR: Personality testing started with ancient Greek doctors blaming your mood on body fluids, got weaponized by two World Wars, was commercialized by a mother-daughter duo with no formal psychology training, and eventually became the internet’s favorite form of self-expression. The science is shaky. The appeal is eternal.

Ancient Greeks Were the Original BuzzFeed

Around 400 BCE, Hippocrates looked at a grumpy patient and thought: too much black bile.

That was the diagnosis. That was the whole thing. The father of Western medicine believed human personality came down to four bodily fluids — blood, yellow bile, black bile, and phlegm — and the balance between them determined whether you were cheerful, aggressive, melancholic, or just… phlegmatic. (That last one literally means “sluggish like mucus,” which is brutal.)

Each fluid mapped to a temperament. Sanguine types were social and optimistic — the life of the ancient symposium. Choleric types were ambitious and short-tempered — your classic Roman general energy. Melancholic types were thoughtful and prone to sadness. Phlegmatic types were calm, reliable, and profoundly unexciting at dinner parties.

Here is the wild part: this framework dominated medicine for nearly two millennia. Galen expanded it in the 2nd century CE, and European doctors were still prescribing treatments based on humoral theory well into the 1800s. Feeling anxious? Bloodletting. Feeling angry? Also bloodletting. The treatment plan was remarkably consistent regardless of the diagnosis.

If you think “which of four types are you?” sounds suspiciously like a BuzzFeed quiz with a medical degree — yeah. That is exactly what it was.

When War Made Personality Testing a Government Priority

The shift from folk wisdom to actual testing happened, like most things in the 20th century, because of war.

In 1917, the United States entered World War I with a problem: they needed to screen 3.5 million recruits, fast, and figure out which ones were psychologically unfit for combat. Psychiatrist Robert Woodworth developed the Personal Data Sheet — essentially a 116-question yes/no checklist designed to flag soldiers at risk of “shell shock” (what we now call PTSD). Questions included gems like “Do you feel like jumping off high places?” and “Are you troubled with the idea that people are watching you on the street?”

It was crude. It was impersonal. It was the first mass-produced personality test in history.

But the real revolution came during World War II, and it did not come from a psychologist. Katherine Cook Briggs had been obsessing over Carl Jung’s 1921 book Psychological Types for two decades, developing her own type theory at her kitchen table. When the war pulled millions of women into the workforce for the first time, Katherine and her daughter Isabel Briggs Myers saw an opportunity: a questionnaire that could match women to jobs suited to their personality type.

Neither of them had formal training in psychology or psychometrics. Isabel developed the MBTI through years of self-funded research, testing it on friends, family, and eventually thousands of medical students. The academic establishment largely ignored her. She kept going anyway.

The irony is thick: the world’s most famous personality test was created by two women who would have been dismissed by the very institutions that later profited from their work. Isabel spent decades fighting for legitimacy, and she died in 1980 still waiting for the psychology establishment to take the MBTI seriously. They never really did. The public, however, had other plans.

Corporate America’s Love Affair With Four Letters

The MBTI exploded in the 1980s and 1990s — not in universities, but in corporate conference rooms. Companies loved it. It was easy to administer, the results were flattering (no type is “bad”), and it gave managers a vocabulary for talking about team dynamics without anyone getting offended. By the mid-2000s, roughly 2 million people were taking the MBTI every year, and 88 of the Fortune 100 companies were using it for hiring, team building, or leadership development.

The scientific community was less enthusiastic. Study after study showed that the MBTI had a retest reliability problem — give someone the test twice, weeks apart, and up to 50% of people get a different type. The binary categories (you are either Introverted or Extraverted, no middle ground) ignored the reality that most personality traits exist on a spectrum. Psychologists had a better model — the Big Five (OCEAN): Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism — backed by decades of rigorous, peer-reviewed research.

But “I score moderately high on Conscientiousness with above-average Neuroticism” does not fit in an Instagram bio. “I’m an INTJ — The Mastermind” does. The MBTI won the culture war not because it was accurate, but because it was narratively satisfying. It gave people a character class, a tribe, a shorthand for the self. Science never had a chance against that.

The Internet Turned Personality Into Content

Then the internet happened, and personality testing went from a niche corporate tool to the backbone of online content.

BuzzFeed understood something powerful in the early 2010s: people will share a quiz result faster than almost anything else on the internet. “Which Disney Princess Are You?” generated hundreds of millions of page views. The quizzes were not scientific — they were barely even coherent — but they tapped into the same ancient itch that Hippocrates scratched with his four humors. Tell me which category I belong to.

The platforms evolved. 16Personalities gave the MBTI a gorgeous visual redesign and a free, accessible test that went massively viral. Co-Star turned astrology into a push notification. The Enneagram found a devoted millennial audience that treated it with the seriousness of actual therapy. TikTok birthed entirely new frameworks — attachment style content, “dark feminine energy” archetypes, love language breakdowns — each one a new lens for the same old question.

What changed was not the question but the stakes. In the social media era, your personality type is not just self-knowledge — it is content. It is your bio, your aesthetic, your brand. Saying “I’m a fearful-avoidant with anxious tendencies” is not a confession anymore; it is an introduction.

And it works. Personality content consistently outperforms almost every other category on social platforms. The reason is simple: identity is the one topic where every single person on earth is a subject-matter expert. You do not need a degree to have opinions about yourself. A history of personality tests meme account can rack up millions of views because the audience is literally everyone who has ever wondered what their “type” is — which is everyone.

The format keeps mutating. In 2024, it is “which celebrity do you share a personality with” videos and AI-generated quizzes. In 2025, it will be something else. The container is disposable. The craving is permanent.

Curious which main character delusion you are actually living? Take our quizzes and find out →

Why Your Brain Craves the Label

There is a name for why all of this works so well, and it is slightly deflating.

The Barnum Effect — named after P.T. Barnum, the circus showman — describes our tendency to accept vague, general personality descriptions as uniquely accurate about ourselves. Psychologist Bertram Forer demonstrated this in 1948 by giving every student in his class the exact same personality profile (pulled from a newspaper horoscope) and asking them to rate its accuracy. Average rating: 4.26 out of 5. They thought it was written just for them. It was not.

But reducing the appeal of personality tests to a cognitive bias misses the bigger picture. Traditional markers of identity — religion, community, lifelong careers — are dissolving. Personality labels fill the gap. They are a handle you can grab onto when everything else feels unstable. You are this, and that is okay, and there are others like you.

Fifty years from now, we will probably look back at MBTI the way we look at bloodletting — quaint, unscientific, kind of funny. And we will still be taking personality quizzes anyway.