Gregory Crewdson, Irving Penn
Larry Fink, James Nachtwey, Boogie, Glen Friedman.
I've come to admire a lot of photography but the name that comes to my mind now is Robert Doisneau.He was the first well know photographer I knew of.
Yousef Karsh and Ansel Adams
Max Dupain, Estevan Oriol & Mario Testino.
I admire Ansel Adams, Arthur Fellig (aka Weegee), David Muench, Elliott Erwitt and Pedro Meyer.
Muybridge for his pursuit of perfection and groundbreaking techniques, The Bechers for their dedication to a systematic approach, Rodchenko for his versatility and creative approach
no one in particular
I can never name just one.
Ernst Haas, Pete Turner, Eric Meola, Freeman Patterson and Jim Erickson. All but the first are alive today, so these may not be what you consider "past masters"
I have a really bad memories for names. I just remember pictures!
I can say there are innumerable masters everywhere I look. Flickr.com is populated with so many talented photographers that I could not choose even one individual artist to point out as the best or most respectable or otherwise notable. The work and depth of talent is awe inspiring.
Having said that, I could not name the "classic" photography masters, even if I was paid to do so.
Well, to be serious for a moment, I really don't like the term "masters of photography." I don't think the photographer "masters" the medium. The photographers I admire are those who engage with the medium in a fluid way. My favorite photographer is Clementina Hawarden -- I wrote a book about her, _Clementina, Lady Hawarden: Studies from Life, 1858 - 1864_, published by Aperture and the V&A Museum, 1999. Photographers whose work I've _always_ liked include Garry Winogrand, Lee Friedlander, William Eggleston, Walker Evans, Harry Callahan, Edward Steichen, Paul Strand, Mario Giacomelli, Larry Burrows, Philip Jones Griffiths, Helen Levitt, William Gedney, John Szarkowski ...