"The Duke" was inspired by the plight of a Lamb of God fan. "A little while ago I became friends with a fan named Wayne Ford - he was terminal - leukaemia. I talked with him often, even video chatted him into the studio," Blythe explained. "He was very calm about his impending death, and we discussed it very openly. I learned a lot from him. This song is for him."

The anthemic rocker finds Randy Blythe singing about mortality. It was originally recorded during the sessions for the band's last album, VII: Sturm Und Drang. Blythe explained to Rolling Stone:

"We had this track that I hadn't finished vocals on, so I wrote it from his perspective. I tried to put myself in his headspace. There's some personal stuff in there that is in his voice and that's to his wife. She'll recognize it. And other stuff was just stuff I drew from our conversation and other stuff was just out of my head. It was just really a way to honor this guy I had gotten to know."

Asked why they titled the song "The Duke", Blythe replied:

"The working title of the song from pre-production was called 'The Hazardous Duke Nukem' because we have idiot working-title names. It was like The Dukes of Hazzard and Duke Nukem. Then we just shortened it to 'The Duke.' So then I wrote these lyrics, and they're serious lyrics. I thought about calling it "Immortalis," which is Latin for immortal. But I was telling Wayne's dad I just like calling it 'The Duke' and he just started laughing. He said he named Wayne after John Wayne. And of course John Wayne's nickname was 'The Duke.' So it's like weird synchronicity."

The song is the title track of The Duke EP, which was released to raise awareness for the Leukemia and Lymphoma Society (LLS) and BeTheMatch, a website operated by the National Marrow Donor Program.

The song marked only the second time in the history of Lamb of God that frontman Randy Blythe used "clean vocals" - actual singing rather than growling or screaming.

"They played it back for me and said, 'Hey, I just wanna tell you something - Randy's singing on this.' And my heart dropped - I've heard him singing on the bus, just goofing off, and it's not good! But obviously, that's just him joking around," bassist John Campbell recalled to The Salt Lake Tribune. "So my heart sank, I was a little nervous, and then the track came on and I was completely blown away. He completely nailed it and effectively used that in his palette for doing vocals."

The only previous time that Blythe used clean singing was on "Overlord," a track that appeared on the band's 2015 album VII: Sturm Und Drang.