Who wrote the music for Battle Hymn of Republic?

The music for the Battle Hymn of the Republic comes from the traditional "John Brown's Body" folk tune.

While the words were written by Julia Ward Howe, the tune itself is much older and has been used for various songs over centuries. The exact origin of the melody is unclear, but it likely originated in the 18th century and was popularized through various uses, including abolitionist songs.