Rex "the Lion" Calabrese was a mob boss in the Gotham underworld before the vigilante known as Batman existed. Calabrese had a daughter named Selina Calabrese who he abandoned when she was nine years old, leaving her to grow up being tossed from foster home to foster home.
The Lion ruled the city before he was pushed out by Carmine "the Roman" Falcone's gang. Deciding to go into hiding, Calabrese adopted the name "Leo Leone" and was sent to Blackgate Penitentiary, no one knowing his true identity as a criminal kingpin. Eventually, when Batman began taking the streets back from the criminals, the Roman, too, went into hiding, allowing for another mob boss to fill the void - the Penguin.
During a play against Batman orchestrated by a mysterious benefactor, Commissioner Jim Gordon was wrongfully incarcerated for murder, being assigned to a cell with "Leo Leone", at the same time that the Roman returned to Gotham and challenged the Penguin for his seat at the top of the underworld. After Falcone and Cobblepot were finally arrested for their crimes, the two attempted to kill each other in Blackgate by starting a riot, prompting Calabrese to finally shed his secret identity. 
Never making an attempt to leave Blackgate, Calabrese instead encouraged his daughter Selina, who was now a full grown adult and went by the alias "Catwoman", to take over the Gotham underworld in his place. With Calabrese's support, Selina made a play and soon became a successful mob boss herself, giving up her life as a costumed thief.
- Calabrese' alias in prison - Leo Leone - used two references to the word 'lion', as Leo and Leone both mean Lion in Latin and Italian.
- 11 Appearances of Rex Calabrese (Prime Earth)
- 1 Images featuring Rex Calabrese (Prime Earth)
- 2 Quotations by or about Rex Calabrese (Prime Earth)
- Character Gallery: Rex Calabrese (Prime Earth)