What was the working title of Metallica's song 'The Four Horsemen'?

The working title of Metallica's song "The Four Horsemen" was "The Mechanix."

The song originated during Dave Mustaine's time in Metallica. Mustaine had written "The Mechanix," and the early Metallica version was performed during the band's formative club shows in 1982. After Mustaine left the group, Metallica substantially reworked the composition for its debut album, Kill 'Em All.

James Hetfield changed the lyrics to focus on the Four Horsemen of the Apocalypse, while the arrangement gained a new bridge and a cleanly picked guitar solo. The result became "The Four Horsemen," one of the album's most distinctive tracks. The song's galloping rhythm and multi-part structure helped showcase Metallica's developing thrash-metal style.

The title can cause confusion because Mustaine later recorded a related song called "Mechanix" with Megadeth. That version retained the original title and was released on Megadeth's 1985 debut, Killing Is My Business... and Business Is Good! Although the two songs share musical DNA, Metallica's version has different lyrics and arrangement, making "The Mechanix" the correct earlier working title.