# Who are some great scientists/mathematicians with not-so-great pre/mid-career credentials?

I am looking for examples of great minds (on any personally defined level) in the history of science and mathematics that had a considerably lesser pre/mid-career reputation/lifestyle/upbringing/etc. Here are a few examples:

I'm particularly looking for people with a not-so-great childhood (i.e. not being a prodigy as a child, growing up in a very poor place, being a delinquent, etc.)

• What I call the "Winston Churchill" question, about a man who did NOT excel in politics--until his old age. Ditto for Abraham Lincoln. – Tom Au Mar 14 '15 at 1:06

One of the most recent famous examples is Yitang Zhang, who proved in 2013 that, if $p_i$ denote primes, then $$\liminf_{n\to\infty} (p_{n+1}-p_n)<7\times 10^7$$ i.e. there are infinitely many primes that are less than $7\times 10^7$ apart. In particular, there are infinitely primes that separated by less than some finite number. This was an amazing breakthrough in number theory, resolving a long-standing conjecture, and using Zhang's methods his result was quickly refined by a large community project that ensued, sharpening the bound to $246$.

Yitang Zhang was 58 when he published his proof, which is regarded as extremely old in the community. He had, up until that moment, had quite an unremarkable academic career, publishing only a single paper in 2001. An interesting profile in the New Yorker details some of his personal life. It explains that Zhang never had much success finding jobs at universities:

His adviser, T. T. Moh, with whom he parted unhappily, recently wrote a description on his Web site of Zhang as a graduate student: “When I looked into his eyes, I found a disturbing soul, a burning bush, an explorer who wanted to reach the North Pole.” Zhang left Purdue without Moh’s support, and, having published no papers, was unable to find an academic job. He lived, sometimes with friends, in Lexington, Kentucky, where he had occasional work, and in New York City, where he also had friends and occasional work. [...] A member of the group [...] opened a Subway franchise as a means of raising money. [...] Zhang kept the books. “Sometimes, if it was busy at the store, I helped with the cash register,” Zhang told me recently. “Even I knew how to make the sandwiches, but I didn’t do it so much.” When Zhang wasn’t working, he would go to the library at the University of Kentucky and read journals in algebraic geometry and number theory. “For years, I didn’t really keep up my dream in mathematics,” he said.

It is clear that Zhang was not regarded as what is known as a 'first-rate mind', much less a prodigy. After his breakthrough paper 'Bounded gaps between primes', Zhang immediately became famous in mathematical circles, receiving a host of prizes, and got to spend time at prestigious academic institution such as the Institute for Advanced Study at Princeton, NJ.