John A. Costello was an American politician who served as the Governor of Maryland from 1947 to 1951. He was a member of the Democratic Party and focused on improving education and public health during his tenure. Costello was known for his efforts to modernize the state's infrastructure and promote economic development. Before becoming governor, Costello held various political positions, including serving in the Maryland House of Delegates. He was also a prominent figure in local politics, contributing to the growth of the Democratic Party in the state. His leadership left a lasting impact on Maryland's political landscape.