Stephen Cole Kleene (January 5, 1909 – January 25, 1994) was an
American mathematician. One of the students of
Alonzo Church, Kleene, along with
Alan Turing,
Emil Post, and others, is best known as a founder of the branch of
mathematical logic known as
recursion theory, which subsequently helped to provide the foundations of theoretical
computer science. Kleene's work grounds the study of which functions are
computable. A number of mathematical concepts are named after him:
Kleene hierarchy,
Kleene algebra, the
Kleene star (Kleene closure),
Kleene's recursion theorem and the
Kleene fixpoint theorem. He also invented
regular expressions, and made significant contributions to the foundations of
mathematical intuitionism.