Ernst Haas and Clifford Coffin are my favorites.
Coffin's story is interesting because he was a character and a half, and also because was very well known and sought after as a fashion photographer in his heyday. But he basically dropped off the face of the Earth and out of common photographic knowledge for various reasons, including his open homosexuality and his being very difficult to work with. He was very brutal on models and a real perfectionist. And how many people were flamingly out of the closet back then? Also, most of his work was destroyed by a vandal who targeted him specifically. The only examples of his work that remain are from the vaults of Vogue, Look, etc...and I think those are mostly prints, not film. On a technical level, he was among the first in the fashion world to make heavy use of color film. He also was a master of making something out of nothing. His props and setups are usually incredibly simple. He perhaps pioneered the use of decayed and destroyed urban structures as backdrops for fashion photography; he was doing this in the '40's with the ruins of post-war Europe. I am pretty sure he didn't invent the ring light, but he popularized it's use for fashion photographs, and built, or at least designed, his own unit. He "discovered" Audrey Hepburn and brought her into the public's eye. I would call him a "lost master" of color photography. He was very forward thinking, and heavily influential on the world of fashion photography to this day.
Haas is interesting because of his weighty career accomplishments (being president of Magnum for a time is among them) and because of his philosophical writing on photography.