The phrase "the greatest thing since sliced bread" denotes any new, convenient and fantastic invention that enters our everyday life. Its origin lies in the 20th century and my favorite first attribution of its use is by comedian Red Skelton telling a Maryland newspaper in 1952 that "television is the greatest thing since sliced bread".
(Red Skelton, phrase inventor)
But someone had to first invent a bread slicer in order for the phrase to have any meaning. For that we need to thank Otto Frederick Rohwedder of Davenport, Iowa. Now bread has been around for thousands of years. Baked in loaves it was sold to customers uncut. Otto was a jeweler, and though I can't find direct confirmation of this, it may be that this background and access to jeweler's blades ignited his imagination about creating a device that could automatically slice bread at the bakery.
(Otto Frederick Rohwedder)
Rohwedder began working on his idea in 1912 and eventually built a prototype which was destroyed in a fire in 1917 which also drove him into bankruptcy. Obsessed by his idea, he refused to give up, finally obtaining financial backing and recreating his machine in 1927 (the patent application for a machine for slicing and wrapping bread was filed on November 26, 1928, U.S. 1,867,377).
The first commercial application of the new slicing machine was by the Chillicothe Baking Company, located in Chillicothe, Missouri, about ninety miles from Kansas City. The company took out ads touting its sliced bread as the "greatest forward step in the baking industry since bread was wrapped." Sliced bread was a gigantic consumer favorite, and was soon adopted by the rest of the industry. Within five years, 80% of American bread was sold pre-sliced. In a serendipitous occurrence, it probably helped that the electric toaster was already invented (in 1909).
The biggest boost for sliced bread was Continental Baking Company's introduction of Wonder Bread in 1930 which became an enormously successful brand.
In 1931, Otto joined the Micro-Westco Co. of Bettendorf, Iowa, becoming vice-president of the Rohwedder Bakery Machine Division. He obtained six more patents, all related to bread slicing. Retiring in 1951, he passed away in 1960 at the age of 80.
The Smithsonian Museum has the original bread slicing machine.