Who is Alan Turing
Alan Turing is one of the most important computer scientists in 20th century. He was born in London and graduated in King's College, Cambridge University. After graduation, he went to Princeton University to continue his study and return to Britain during the outbreak of World War II. His study of encryption has contributed to winning of the war. He's other studies has been recognized as fundament of modern computer science.
Crack the Enigma 
During the World War II, German army use an enciphering machine called Enigma to encrypt secret messages. In order to decrypt German secret messages, Turing and his colleagues invented a electromechanically decryption machine named Bombe. It works more efficient than any other decrypt machines at that time. With the help of Bombe, German Air Force messages was read by Britain Army from mid-1940. After the war, Turing was granted Order of The British Empire (OBE) for his contribution in the war.
Turing Machine 
In 1936, Turing introduced a general-purpose computing machine. It is a mathematical abstraction of modern computers. With this abstraction, Turing proved the halt problem is not solvable, hence there exists problem that can't be solved by computing machines. Although Turing machine can't solve any problems in the universe, Turing has proved it can solve any problems that human can do. If a computation system satisfy the requirement of Turing machine, then it is called “Turing Complete”, all modern computers are an implementation of Turing machines.
Turing and AI 
Turing was also the pioneer scientist to study artificial intelligence. In 1950, he proposed an imitation test to examine whether a machine can exhibit intelligent behavior equivalent to a human. Today, this set of tests is known as Turing test. Although scientists have proposed other tests as AI studying making progress. Turing test is still the most well-known for detecting whether machines have intelligence.
Turing is the computer scientist I admire the most. When looking at the works of him, I am impressed by his intelligent and his contribution to humankind.