The WABAC machine was a central element of the Peabody's Improbable History cartoon segment. The machine was invented by Mr. Peabody, a genius, polymath, and bow tie-wearing beagle, as a birthday gift for his adopted pet boy, Sherman. By allowing them to visit famous historical people or events, the WABAC provided educational adventures for Sherman. At the request of Mr. Peabody ("Sherman, set the Wayback machine to ..."), Sherman would set the WABAC controls to a time and place of historical importance, and by walking through a door in the WABAC machine, they would be instantly transported there. Examples of places or people visited are the Marquess of Queensberry and the rules of boxing, the imprisonment and memoirs of Casanova,and Jim Bowie and the Bowie knife. The machine apparently later returned Mr. Peabody and Sherman to the present, although the return trip was never shown. The segment traditionally ended with a pun.
Either of the names WABAC or Wayback are in common usage, with the term "WAYBACK" explicitly indicated during the segment in which Mr. Peabody and Sherman visit the "Charge of the Light Brigade". The precise meaning of the acronym WABAC is unknown. According to Gerard Baldwin, one of the show's directors, the name "WABAC" is a reference to the UNIVAC I. Mid-century, large-sized computers often had names that ended in "AC" (generally for "Automatic/Analogue Computer" or similar), such as ENIAC or UNIVAC. The term "Wayback" suggests the common expression "way back in some former time."