Rex Calabrese was a crime boss who dominated the Gotham underworld decades ago. His scarred face and use of fake razor sharp fangs earned him the alias the Lion, a persona which helped him rise to prominence in the mob during a time before criminals wore costumes, masks or face paint. Calabrese believed that there was a Natural Order to crime and that one day, much like he had done to the previous mob boss, an up and coming gangster would depose and kill him. It was rumored that Carmine Falcone fulfilled this prophecy, but while Calabrese lost control of the underworld to Falcone, he was not killed but instead incarcerated in Black Gate prison.

Years later, Jim Gordon was jailed for his role in a subway crash and ended up sharing a cell with Calabrese. During a prison riot both men worked together to maintain order and minimize death. After the riot, Selina Kyle broke into Black Gate to meet with the Lion and during their discussion he encouraged her to seize power and unify the crime families under her leadership.