Danny Sugerman, manager of rock band The Doors, has died aged 50 in Los Angeles after battling lung cancer.
Densmore described Mr Sugerman as the "number one Doors fan"
Mr Sugerman became involved with the legendary group in the late 1960s at the age of 14 and eventually became the reformed group's co-manager.
Mr Sugerman co-wrote the 1980 Doors biography No One Here Gets Out Alive with music journalist Jerry Hopkins.
The Doors are best known for songs such as Light My Fire and Riders on the Storm. Singer Jim Morrison died in 1971.
Doors drummer John Densmore said: "Danny was the number one Doors fan of the world. I told him no-one loved Jim as much as he did."
After seeing them perform as a teenager, Mr Sugerman took on the task of answering the band's fan mail and Morrison later suggested he should become a management associate.
Mr Sugerman also worked as technical advisor on 1991 film The Doors which portrayed their hedonistic rock lifestyle.
He managed Doors guitarist Robby Krieger, keyboard player Ray Manzarek and drummer John Densmore after Morrison died.
Manzarek said: "Danny is standing side-by-side with his great friend, Jim Morrison, and the two of them will now be laughing together into eternity."
Manzarek and Krieger have been touring as The Doors of the 21st Century with former The Cult singer Ian Astbury since 2002.