Photographer. Known especially for images of the Civil War and its aftermath, he also documented the West and created notable portraits. Born in Paisley, Scotland, as a young man he worked as a jeweler in Glasgow. Drawn to literature and issues of social welfare, he became a follower of utopian socialist Robert Owen; in 1850 he traveled to Iowa with his brother James Gardner (1829–?), later also a photographer, to purchase land for a cooperative community. Subsequently in Glasgow he worked as a reporter and editor, while also becoming interested in photography. Intending to settle in Iowa, he traveled there in 1856 but soon left for New York. There he found employment in Mathew B. Brady's studio, where his technical skill with the new glass negative technology proved particularly valuable. In 1858 Brady put him in charge of his Washington operation, which prospered under Gardner's artistic direction and canny management. When the Civil War broke out, Gardner worked on Brady's project to document the conflict. After they quarreled over Brady's practice of issuing his reporters' work under his own name, in 1863 Gardner opened a rival Washington studio in partnership with his brother. Among Alexander's subsequent portraits, several important images of Abraham Lincoln included the last, taken only days before his death. He also compiled his own record of the ongoing war. As official photographer for the Army of the Potomac, he enjoyed access to major events and military staff. As Brady did, he hired other photographers to contribute to his Civil War archive but always scrupulously credited their work. His own contributions include many of the strongest and most affecting images of the war. After the surrender, he continued to pursue newsworthy events. His moving series portraying the conspirators in Lincoln's assassination and their public execution ranks among photojournalism's earliest pictorial essays. In 1866 he published a lavish, two-volume Photographic Sketch Book of the War, illustrated with one hundred tipped-in original photographs by Gardner and others. Each was accompanied by a text presumably composed by Gardner. In 1867 Gardner traveled west for the Union Pacific Railroad, and in this capacity recorded landscapes, townscapes, and local features, as well as rail construction. He also photographed the West's Indian inhabitants, particularly those attending an 1868 peace conference in Laramie, Wyoming. He died in Washington.