Felix Hernandez pitched the 23rd perfect game in baseball history. It was the 21st of the modern era (post-1900), and the third of the 2012 season. Read that last sentence again ... this just doesn't make sense. It's an every-two-month thing now.
A list of perfect games in baseball history:
Lee Richmond - 6/12/1880
John Ward - 6/17/1880
Cy Young -5/05/1904
Addie Joss - 10/02/1908
Charlie Robertson - 4/30/1922
Don Larsen - 10/08/1956
Jim Bunning - 06/21/1964
Sandy Koufax - 9/09/1965
Catfish Hunter - 5/08/1968
Len Barker - 5/15/1981
Mike Witt - 9/30/1984
Tom Browning - 9/16/1988
Dennis Martinez - 7/28/1991
Kenny Rogers - 7/28/1994
David Wells - 5/17/1998
David Cone - 7/18/1999
Randy Johnson - 5/18/2004
Mark Buehrle -7/23/2009
Dallas Braden - 5/09/2010
Roy Halladay - 5/29/2010
Philip Humber - 4/21/2012
Matt Cain - 6/13/2012
Felix Hernandez - 8/15/2012
Felix's perfect game was the first in Mariners history, and the fourth no-hitter in franchise history. Six Mariners pitchers combined to no-hit the Los Angeles Dodgers on June 8.
Armando Galarraga lost his perfect game on a blown call at first base, and then he retired the next hitter. Two pitchers -- Harvey Haddix and Pedro Martinez -- were perfect through nine innings (with Haddix perfect through 12) before losing the perfect game and the game in extra innings.