In February 2014, Metallica began recording a new song at their HQ studio in San Rafael, California, with the working title "X-Dust", planning to premiere it at a March 16, 2014, show in Bogotá, Colombia. They finished it in March and premiered it at the show with the official song title "Lords of Summer".[1] The band re-recorded the song in May and June 2015 for their tenth studio album, Hardwired... to Self-Destruct (2016),[1] including it with the deluxe edition of the album. It is over a minute shorter in length than the demo and first pass versions.[2]
According to drummer Lars Ulrich, the song was inspired by the band's then upcoming 2014 tour, as he explained in an interview given to Metal Hammer magazine: "It's about being outdoors and festivals and here we are again."[3] Being an uptempo thrash metal song much in the vein of Metallica's earlier works from the 1980s and being self-referential in nature in terms of its lyrical content, the song alludes to a number of now 'classic' tracks from that particular period, most notably "The Four Horsemen" and "No Remorse" (both from 'Kill 'em All', 1983): "Pounding, pounding, no remorse / Lords of summer set on course / Pushing, pushing horsemen ride / Lords of summer undenied".
The band released the song digitally through the iTunes Store on March 19, 2014, in its demo form.[4] They eventually released the song in a more refined state, dubbed the "First Pass Version", digitally in June.[5] Later that year, they gave the song a physical release for Record Store Day Black Friday as a 12-inch single, with a live version of the song recorded in Rome being used as the B-side. The single was limited to 4,000 copies.[6] A remix of the song by The Glitch Mob was released on May 13, 2015, through YouTube.[7]