Roussos was as famous for his outfits as his
Greek singer Demis Roussos, who sold more than 60 million albums worldwide, has died aged 68 the Hygeia Hospital in Athens has confirmed to the BBC.
He was best known for his solo hits in the 1970s and 80s, including Forever and Ever, Goodbye and Quand je t'aime.
He was also a member of progressive rock group Aphrodite's Child.
Roussos was renowned for his off-screen role in Mike Leigh's 1977 TV play Abigail's party, having provided the party's soundtrack.
He had been in the private hospital with an undisclosed illness for some time.
The singer was born Artemios Ventouris Roussos in Alexandria, Egypt, in 1946, to a Greek father and Egyptian mother of Italian origin.
He was raised there until his parents moved to Greece in the early 60s after losing their possessions during the Suez Crisis.
Roussos began his music career at 17, when he joined the a band called The Idols, where he met his future Aphrodite's Child bandmate Vangelis.
Aphrodite's Child produced three albums and enjoyed huge success in Europe in the late 1960s, especially France.
Roussos went on to have a solo career, and Forever And Ever topped the charts in several countries in 1973 and in the UK in 1976.
Other hits include My Friend the Wind, My Reason, Someday Somewhere and Happy To Be On An Island In The Sun.
Roussos' fondness for kaftans saw him dubbed "the Kaftan King" and he often wore them for his performances on shows such as Top of the Pops.