Justin Whitlock Dart, Sr. (August 7, 1907 - January 26, 1984) was considered the "boy wonder" of the drug store industry. In college Dart had played football for Northwestern University, where he was an All-American.

Dart was an heir to the Walgreen's Drugstore chain, which his wife Ruth Walgreen 's father Charles Walgreen had founded. At Walgreen's he innovated by placing the pharmacy counter at the back of the drug store, both providing privacy for customers, and forcing them to walk past many items for possible purchase.

He took control of Boston, Massachusetts based United Drug Company in 1943. The chain operated under Ligget, Owl, Sonta, and Rexall brands, and he rebranded the stores under the Rexall name.

He sold his stake in Rexall in 1978 though Dart had acquired stakes in Avon, West Bend, Duracell, Hobart, and Ralph Wilson Plastics and Archer Glass , which were collectively Dart Industries (later Premark International ). Dart was part of Ronald Reagan's "kitchen cabinet ". His son Justin Whitlock Dart, Jr. was an advocate for the disabled and helped pass the Americans with Disabilities Act.