LONDON — Musician Greg Lake co-founded both King Crimson and Emerson, Lake and Palmer — bands that helped define the sprawling, influential but often-maligned genre known as progressive rock. Mr. Lake, who died of cancer at 69, was instrumental in bringing classical influences, epic length, mythic scope and 1970s excess into rock ’n’ roll, winning millions of fans before punk swept in and spoiled the party. With Mr.