Ian Chase was a socialite and presumed mobster, as well as a murderer.
During a Halloween Party at Wayne Manor, Ian Chase ended up causing a disturbance (presumably by harassing Clarissa Rodriguez, based on a comment made by Alfred), which forced Bruce Wayne to throw him out. Two months later, on Christmas Eve, Chase, by that time, a gang member to The Joker (who had taken over Black Mask's Gang) went to Crime Alley and proceeded to murder both Rodriguez and her fiancée, Horace Riley, by shooting her in the heart, and shot him in the lung, respectively, coincidentally at the same spot where Bruce's Parents had been murdered during a mugging during Bruce's childhood (it's implied that Chase did that out of a grudge from a unrequited love triangle, where Clarissa went with Horace instead of him). Although Chase had managed to clean up the area by removing most of the bullet casings, he missed one inside of the grate. Batman, Bruce Wayne's alter ego, managed to uncover the murder and deduced Chase's role in their murder. Batman then tracked Chase down to the Industrial District, where Chase, alongside other mobsters were discussing his role in the murder (dialogue suggested that he would have been the number one suspect in Riley and Rodriguez's murders, but could not be convicted without proof). Batman then ended up attacking Chase and nearly killed him due to his petty reason for committing the murders before Alfred calmed him down.
- It was suspected that Ian Chase was part of either Black Mask's or the Joker's Gang, due to both his presence at the Sionis Steel Mill when Batman apprehended him as well as his wearing a clown mask (which was what all of Black Mask's Gang members started to wear after Joker openly revealed himself to have taken over Black Mask's operations).
- It's possible that the reason that Batman nearly killed Ian Chase was because in his Detective Mode, we saw Bruce's Parents on the ground for a brief moment when Ian shot Horace and Clarissa, which reminded him of his Parents' Deaths, since Crime Alley was where his parents died.