Robert Gregg "Bob" Koester (born October 30, 1932) is the American founder and owner of Delmark Records, the oldest jazz and blues independent record label in the United States and one of jazz's best-known imprints. He also operated the Jazz Record Mart in Chicago, formerly the world's largest jazz and blues record store.
Koester was born and grew up in Wichita, Kansas, during the heyday of big band jazz. He started collecting and then trading records in his high school years. Wanting to become a movie cameraman, he moved to St. Louis, Missouri, to study cinematography and business at Saint Louis University, where he sold records by mail order from his dormitory room. He was a founding member of the St. Louis Jazz Club, through which he met Ron Fister, another record collector. Koester and Fister opened a small record store, K & F Sales. On moving to bigger premises they renamed it Blue Note Record Shop. After nearly a year together, Koester and Fister decided to split their business and Koester founded Delmar Records, on Delmar Blvd. Delmar first recorded a traditional jazz group in 1953 and then searched out and recorded blues musicians of the 1920s and 1930s (Speckled Red, Big Joe Williams, J.D. Short, and James Crutchfield among others) who were living in St. Louis. The name of the label was changed from Delmar to Delmark, partly because of copyright issues.
Koester moved to Chicago in 1958. He purchased Seymour's Jazz Mart, in the Roosevelt University Building, from Seymour Schwartz in 1959. In 1963, he relocated the Jazz Record Mart and Delmark Records to 7 West Grand Avenue. In 1971, he purchased premises at 4243 N. Lincoln Avenue and moved Delmark there.
In 1996, Koester was inducted into the Blues Hall of Fame.