This song is a tribute to late Motorhead frontman Lemmy Kilmister. Speaking during an interview on Sirius XM, vocalist James Hetfield said:
"Motorhead had a lot to do with Metallica sitting here right now. Lemmy as an entity - a kind of father figure - helped us a lot. He was unafraid and he was a character. And he was himself. We all respected that so much. He did his own thing to the last breath. No matter who you are, how could you not be inspired by that?"
Lars Ulrich explained how following Motorhead around on tour as a fan helped him want to take Metallica seriously. The drummer said: "When I came back to Southern California, I called James up and said: 'Listen, we've got to give this a shot.' Motorhead is the catalyst."
"Murder One" was the name of Lemmy's favorite amplifier on stage. Speaking to Gary Moore of the 95.5 Klos radio station, James Hetfield said of the amp. "I loved being murdered every night by that thing, man."
"He was just such an icon, such an inspiration to us as a band," Hetfield added regarding the late Motorhead frontman. "There's certainly no way we'd be around if there was no Motörhead. And, you know, to see your idol, your immortal one, actually be mortal, it hit us pretty hard. So I felt, lyrically, it makes sense to acknowledge him and how much he's meant in our lives."
Metallica and Motorhead have a shared history. During a 1995 gig at the Whisky A Go Go in Hollywood, members of Metallica celebrated Lemmy's 50th birthday by taking the stage as a wigged tribute band dubbed the Lemmys. Ten years later, Motorhead won the 2005 "Best Metal Performance" Grammy for their cover version of the Metallica song "Whiplash
The song's animated music video was directed by Robert Valley, who is best known for his animation work on Gorillaz's music videos and the Tron: Uprising TV series. The clip tells the story of Lemmy’s career from his early days with Hawkwind. It incorporates some of the late Motorhead frontman's most iconic imagery such as his trademark bass rifle pose.