  This review describes the events leading up to the discovery of the Kerr
metric in 1963 and the enormous impact the discovery has had in the subsequent
50 years. The review discusses the Penrose process, the four laws of black hole
mechanics, uniqueness of the solution, and the no-hair theorems. It also
includes Kerr perturbation theory and its application to black hole stability
and quasi-normal modes. The Kerr metric's importance in the astrophysics of
quasars and accreting stellar-mass black hole systems is detailed. A theme of
the review is the "miraculous" nature of the solution, both in describing in a
simple analytic formula the most general rotating black hole, and in having
unexpected mathematical properties that make many calculations tractable. Also
included is a pedagogical derivation of the solution suitable for a first
course in general relativity.
