"Four Horsemen" by artist and musician John Baizley (of the band Baroness). Baizley created the piece for Revolver's 2011 collector's issue dedicated to Metallica, Slayer, Megadeth, and Anthrax. Baizley's art was so popular with the band that James Hetfield purchased the original for his collection, and Metallica licensed the image. Baizley reworked the piece with additional color (seen here) for the "Four Horsemen" t-shirt design. He later told Revolver, "When I was a teenager, I would have killed someone in broad daylight to get my art on a Metallica shirt."
From the Collection of James Hetfield