Johnny “Big Moose” Walker (June 27, 1927 – November 27, 1999) was an American Chicago blues and electric blues pianist and organist. He worked with many blues musicians, including Ike Turner, Sonny Boy Williamson II, Lowell Fulson, Choker Campbell, Elmore James, Earl Hooker, Muddy Waters, Otis Spann, Sunnyland Slim, Jimmy Dawkins and Son Seals.

Walker was primarily a piano player but was also proficient on the electronic organ and the bass guitar (he played the bass guitar when backing Muddy Waters). He recorded solo albums and accompanied other musicians in concert and on recordings.

John Mayon Walker was born in the unincorporated community of Stoneville, Mississippi, partly of Native American ancestry. He acquired his best-known stage name in his childhood in Greenville, Mississippi, derived from his long, flowing hair.