Among his hired staff were Alexander Gardner and Timothy H. O'Sullivan
This man began to collect portraits of famous people in 1845, eventually compiling them into his 1850 A Gallery of Illustrious Americans.  At the outbreak of the American Civil War, he embarked on a project that costed $100,000 and would eventually bankrupt him.  Among his hired staff were Alexander Gardner and Timothy H. O'Sullivan (*) and 20 others, each of whom were given a mobile darkroom, capturing scenes of Civil War battlefields, including shots of Antietam which were exhibited in "The Dead of Antietam".  FTP -- Name this pioneering American photographer, who took the pictures of every president from John Quincy Adams to William McKinley.
This man began to collect portraits of famous people in 1845, eventually compiling them into his 1850 A Gallery of Illustrious Americans.  
Mathew {Brady}