Union Pacific 844 is a class "FEF-3" 4-8-4 "Northern" type steam locomotive owned and operated by the Union Pacific Railroad for its heritage fleet. Built in December 1944 by the American Locomotive Company (ALCO) of Schenectady, New York, No. 844 is one of four surviving FEF series locomotives and the only one in operation.

The Union Pacific FEF series consists of 45 4-8-4 "Northern" steam locomotives built by the American Locomotive Company (ALCO) between 1937 and 1944 and operated by the Union Pacific Railroad until 1959. Like other Union Pacific steam classes, the acronym comes from the first letter of the spelling of its wheel arrangement: Four Eight Four.