Ian McDonald, a multi-instrumentalist and songwriter best known for his co-founding roles in both King Crimson and Foreigner, died Wednesday at the age of 75. A rep for McDonald confirmed the musician's death, adding that McDonald "passed away peacefully on February 9, 2022 in his home in New York City, surrounded by his family." His son reported on Facebook that the cause was cancer.

McDonald was known as one of the key architects of progressive rock, playing both saxophone and keyboards in King Crimson and co-writing its iconic 1969 debut, In the Court of the Crimson King. The record's opening track, "21st Century Schizoid Man," featured McDonald's wild double-tracked alto-sax solo, which he performed the same year at a famous concert in London's Hyde Park. He left King Crimson before the year was over, moving on to a duo project with Crimson drummer Michael Giles. He would also appear as a session musician on King Crimson's 1975 classic, Red.

Later, McDonald co-founded rock outfit Foreigner with guitarist Mick Jones, playing various instruments and singing on their first three LPs — all of which cracked the Top 10.

McDonald also performed as a session saxist on T. Rex's classic 1971 album, Electric Warrior, and later reunited with part of the original Crimson lineup as a member of the 21st Century Schizoid Band. His final major project was the rootsy rock band Honey West.