Short answers, pulled from the story.
Mathew Brady (c. 1822-1896) was an American photographer best known for documenting the Civil War through tens of thousands of photographs. He is credited as the father of photojournalism and created the most important visual record of the Civil War, now held in the National Archives and the Library of Congress.
Brady applied first to General Winfield Scott and then to President Abraham Lincoln, who granted permission in 1861. Lincoln's condition was that Brady finance the entire project himself, which Brady agreed to at a personal cost of over $100,000.
The Dead of Antietam was an October 1862 exhibition at Brady's New York City gallery displaying graphic photographs of corpses from the Battle of Antietam. The images were taken by Alexander Gardner and James Gibson on the 19th of September, 1862, two days after the battle. It was the first time many Americans saw battlefield photographs of the dead rather than painted depictions.
Brady photographed 18 of the first 19 American presidents, from John Quincy Adams to William McKinley. The only exception was William Henry Harrison, who died in office three years before Brady began his photographic work.
Brady spent over $100,000 documenting the Civil War expecting the U.S. government to purchase the photographs afterward. The government declined, and private collectors showed little interest in war imagery. Brady was forced to sell his New York studio and file for bankruptcy. Congress granted him $25,000 in 1875, but he remained in debt and died penniless on the 15th of January, 1896.
Many of the photographs attributed to Brady were taken by his team of assistants, including Alexander Gardner, Timothy H. O'Sullivan, and George N. Barnard. Brady generally stayed in Washington organizing assignments and rarely visited battlefields. Every image from his studio was labeled "Photo by Brady" regardless of who operated the camera, a practice for which he was criticized.