The Turing machine
Turing imagined a simple machine that reads and writes symbols on an infinitely long tape according to a table of rules. He showed that such a machine can carry out any computation that can be described as a procedure. Every processor, phone and games console is, in this sense, a universal Turing machine.
Enigma
At Bletchley Park he designed the electromechanical Bombe machines, which searched for Enigma's daily settings. The decrypted messages helped the Allies, especially in the fight against U-boats in the Atlantic. Modern cryptography, which today protects the encrypted internet, grew out of this work.
Can machines think?
In 1950 he proposed a test, known today as the Turing test: if a person cannot tell a machine from a human in a written conversation, we can say the machine thinks. The question is being asked again today, about today's language models.
Recognition, too late
In 1952 he was convicted for homosexuality, which was a criminal offence in Britain at the time. He died two years later. The British government apologised to him in 2009, he received a royal pardon in 2013, and since 2021 he has appeared on the £50 note.