# 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 $246$.