Alan Turing was one of the most brilliant mathematicians of the Twentieth Century -- indeed, one of most brilliant mathematicians ever. During World War II he was instrumental in breaking the Nazi's "Enigma" code. In the process, he developed much of the theoretical framework for the field of computer science. The mathematical model of computers that every comp sci major learns about, the "Turning machine", was his invention. Every time you use a computer -- such as reading this -- you are benefiting from his genius.
But let's get back to the fact that he helped defeat the Nazis and thus helped save the UK, and all of Western civilization.
Usually, people who help save a nation are treated with gratitude. But Turing was gay.
In the homophobic society in which he lived, that was a crime. His security clearance was revoked, he was prosecuted, and sentenced to "chemical castration" via hormone injections. In 1954, he committed suicide.
Over 55 years later, the UK has finally apologized for its wretched treatment of this heroic genius.