Sliced bread was first sold in 1928 and advertised as “the greatest forward step in the baking industry since bread was wrapped”. This led to the popular phrase, “the greatest thing since sliced bread”.
Otto Frederick Rohwedder of Davenport, Iowa, USA invented the first loaf-at-a-time bread-slicing machine. A prototype he built in 1912 was destroyed in a fire and it was not until 1928 that Rohwedder had a fully working machine ready. The first commercial use of the machine was by the Chillicothe Baking Company of Chillicothe, Missouri, which produced their first slices on July 6, 1928.
Source: Wikipedia, City of Chillicothe