As a collector of fine art photography, I think that Duane Michals (1932 - present) is one of the most important fine art photographers of the second half of the 20th century.  He is given credit for two significant developments in 20th century photography:  [1] telling stories through a series of related photographs (sequences), and [2] handwriting text near his photographic images, giving more meaning to the photographic image.  Other artists have since followed his lead to also create a sequence of photographs to tell a story, and to handwrite on their photographs as part of the artistic statement.  But Duane Michals is given credit for being the first.