John Chalmers MacGregor (March 28, 1903 – March 9, 1973), better known as Chummy MacGregor, a musician and composer, was the pianist in The Glenn Miller Orchestra from 1936 to 1942. He composed the songs "Moon Dreams", "It Must Be Jelly ('Cause Jam Don't Shake Like That)", "I Sustain the Wings", "Doin' the Jive", "Sold American", "Cutesie Pie" in 1932 with Bing Crosby and Red Standex, and "Slumber Song".