His music labels, Cherry Red Records and Esoteric Recordings, announced the death but did not disclose the cause. Mr. Thomas said in 2014 that he had been diagnosed with prostate cancer.
Mr. Thomas performed in rock and blues bands in the English city of Birmingham before founding the Moody Blues in 1964 with fellow musicians including keyboardist Mike Pinder and guitarist and singer Denny Laine.
The band's roots lay in blues and R&B, but its 1964 cover of Bessie Banks's "Go Now" was a foretaste of the lush, orchestral sound that came to be called progressive rock.
Their 1967 album "Days of Future Passed" is considered a prog-rock landmark, and featured a signature flute solo by Mr. Thomas on the single "Nights in White Satin." The album was credited as a model for popular 1970s groups such as Yes, Genesis and Supertramp.
Raymond Thomas was born in Stourport-on-Severn, near Birmingham, on Dec. 29, 1941. He sang in a choir as a teenager and was inspired to learn the flute from a grandfather who played the instrument, according to the website All Music.
Mr. Thomas wrote several songs for the Moody Blues, including the trippy "Legend of a Mind" and "Veteran Cosmic Rocker," and released two solo albums after the band broke up in 1974. The Moody Blues later reformed, and Mr. Thomas remained a member before leaving in 2002 because of poor health.
Notable deaths in 2017
He married Lee Lightle in 2009. A complete list of survivors was not immediately available.
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