He was 70.
"It is with the heaviest hearts we heard that our beloved Joe Cocker passed away last night," Barrie Marshall said in a statement to the BBC. "He was without the doubt the greatest rock/soul voice ever to come out of Britain and remained the same man throughout his life. Hugely talented -- a true star -- but a kind and humble man who loved to perform. Anyone who ever saw him live will never forget him."
Cocker, who was born John Robert Cocker in 1944, rose to fame in the 1960s when he covered "With a Little Help From My Friends" by the Beatles. His version was later used as the theme song for the series "The Wonder Years."
In 1975, he enjoyed another hit with "You Are So Beautiful," before winning a Grammy in 1983 for a duet of "Up Where We Belong" with Jennifer Warnes. He last released an album, "Fire It Up," in 2012 and had been performing live last year.
"I think he should be in the Rock and Roll Hall of Fame," his friend Billy Joel said in September, calling Cocker "a great singer who is not very well right now." "I’m amazed that he’s not yet."
Cocker is survived by his wife, Pam Baker, with whom he lived on a ranch in Colorado. The couple did not have children.
"He was simply unique," Marshall, who has not yet responded to ABC News' request for comment, added in the statement. "We had the joy to work with this wonderful man for almost 30 years. We loved him, and it will be impossible to fill the space he leaves in our hearts."