Harvey Dent is a comic book character who made his debut in Detective Comics #66 in August 1942. Known as a tough prosecuting attorney, he ran afoul of the Maroni family ultimately leaving his face disfigured and with a split personality. The dark personality would become known as the villain Two-Face. He is best known for flipping a coin and letting the heads/tails result determine his adversary's fate.
Ian and John Hargrove are brothers in this episode. Ian is the Scottish form of the name John. So the brothers essentially have the same name.