Agent Andrew Goodfriend tells The Associated Press that Kilmister died on Monday in Los Angeles after a brief battle with aggressive cancer.
And the band posted the news on their Facebook page, "There is no easy way to say this... our mighty, noble friend Lemmy passed away today after a short battle with an extremely aggressive cancer."
Known simply as "Lemmy" to most, he was as famous for his mustache, mutton chops and the mole on his face as his music.
But he was deeply respected and revered as a rock master and innovator, from his time with the seminal psychedelic band Hawkwind in the early 1970s to his four decades in Motorhead, best known for their 1980 anthem "Ace of Spades."
Each of the band's legendary live shows would begin with Kilmister's loud announcement: "We are Motorhead! We play rock and roll!"
Celebrities have taken to social media to comment on their friend's passing.
Lost one of my best friends, Lemmy, today. He will be sadly missed. He was a warrior and a legend. I will see you on the other side.— Ozzy Osbourne (@OzzyOsbourne) December 29, 2015
Farewell Lemmy. I love you brother.— Dave Mustaine (@DaveMustaine) December 29, 2015
Lemmy: Rest In Peace. Shake the heavens, my friend.— Gene Simmons (@genesimmons) December 29, 2015
Lemmy: Rest In Peace, my friend. pic.twitter.com/2M6VPiBGyE— Gene Simmons (@genesimmons) December 29, 2015
Oh my. Lemmy got let in on the big secret. One of the greatest rockers of all time. Amazingly unique incredible bass player. My hero. Wow.— Flea (@flea333) December 29, 2015
My dear friend, Lemmy, passed away today. I’ve known him for 38 years. He will be so missed but he will never be forgotten.— Sharon Osbourne (@MrsSOsbourne) December 29, 2015
Sorry to hear Lemmy Kilmister has passed away. Grateful for the few brief momentsJay and I spent with him. Condolences to friends and family— Tom Hamilton (@THaerosmith) December 29, 2015
Oh my god, Lemmy. What a hell of a ride you had. Nobody came close being the Rock God THAT YOU ARE. Shedding tears of metal for you Bud.— butchwalker (@butchwalker) December 29, 2015
IN MEMORIAM 2015: Celebrities and notable figures who have died
The Associated Press contributed to this report.