Guitarist had been diagnosed with dementia in 2014, when he had been forced to retire from the band.

Malcolm Young—one of rock's greatest rhythm guitarists of all time—died today at age 64. The AC/DC co-founder was diagnosed with dementia in 2014, when he was forced to retire from the band.

"Today it is with deep heartfelt sadness that AC/DC has to announce the passing of Malcolm Young," AC/DC wrote in a statement.

"Malcolm, along with Angus, was the founder and creator of AC/DC. With enormous dedication and commitment he was the driving force behind the band. As a guitarist, songwriter and visionary he was a perfectionist and a unique man. He always stuck to his guns and did and said exactly what he wanted. He took great pride in all that he endeavored. His loyalty to the fans was unsurpassed."

Angus Young, Malcolm's younger brother, added: "As his brother, it is hard to express in words what he has meant to me during my life, the bond we had was unique and very special. He leaves behind an enormous legacy that will live on forever. Malcolm, job well done."

Malcolm's skills as a guitarist—and his importance to AC/DC—have never been underestimated.

Throughout AC/DC’s 41-year history, Angus always wrote and recorded the band’s albums in close collaboration with Malcolm, whose monumentally solid rhythm guitar playing and gift for playfully dirty lyrical innuendo has been the band’s backbone. But when Malcolm fell victim to his debilitating condition, Angus found himself alone at the helm of a band that has become a much revered rock and roll legend.

In an additional statement, the band added that Malcolm died peacefully with his family by his side. "Renowned for his musical prowess, Malcolm was a songwriter, guitarist, performer, producer and visionary who inspired many. From the outset, he knew what he wanted to achieve and, along with his younger brother, took to the world stage giving their all at every show. Nothing less would do for their fans."