Like many folk songs, "John Henry" was passed from singer to singer by word of mouth long before it was ever recorded. As a result, there's more than one set of lyrics and more than one musical arrangement.
While a folk rendition of the song may be the most well known, there are also blues and country versions that are possibly just as old. And over the song's long history, it has also served as an anthem for union workers and radical political organizations such as the Communist Party.
Originally, though, the song functioned as a work song. Railroad workers sang it to set a pace as they labored on the tracks. And ironically, workers most commonly sang it slowly. The song may have celebrated a steel-driver who worked himself to death in a high-speed race against a machine, but workers managed to celebrate Henry's victory and learn the song's darker lesson: that back-breaking labor could kill a man—take it slowly or a man could die.