Joe Chill was a robber better known as the killer of Thomas and Martha Wayne during an attempt to take their money and jewelry in Crime Alley. Thus, this traumatic event caused young Bruce Wayne, the only survivor of the attack, to become the vigilante known as Batman.
Before Arkham Origins Incident
Joe Chill was a lowly mugger who attacked the Wayne Family one night on their way home from the Monarch Theatre. Although Chill only wanted their money and jewelry, things quickly escalated out of control when Thomas Wayne tried to fight him.
This ended when Chill shot both Thomas and Martha Wayne dead before he vanished into the night, and left their only son, Bruce, alive, although not before taunting the boy by claiming that "try [and] be a hero" will get one killed while citing Thomas as an example. Joe Chill's actions haunted Bruce Wayne for the rest of his life and ultimately put him on the path to becoming the city's savior: Batman.
Arkham Origins Incident
Joe Chill was seen physically shooting Thomas and Martha Wayne in front of Bruce during a flashback in the Batcave after he returned from the Royal Hotel, with it also being implied that Batman mentally compared the sheer level of the then-new kingpin The Joker's depravity as being similar to Chill. He was also indirectly mentioned in the final casefile mission in the game, Crime Alley Shootings, where Batman noticed the similarities between the death of Clarissa Rodriguez and Horace Riley to the murder of his own parents, and it was implied that his nearly killing Ian Chase was due to his projecting Joe Chill onto him.
Arkham Asylum Incident
Chill's voice was heard in the second Scarecrow Nightmare when he shot Thomas and Martha Wayne.
Arkham City Incident
While Joe Chill didn't make any appearance in the game, Crime Alley (where he attacked and killed Thomas and Martha Wayne) did.
Arkham Knight Incident
Like before, Joe Chill didn't make an appearance, but he was briefly alluded to when several Joker hallucinations, while goading Batman into using a "gun" on Scarecrow, stated that Scarecrow was no different than "the freak who killed your parents."
- Oddly, when Batman hallucinates the memory of Chill in the first game, the voice of Thomas implied that he was complying with the mugger and got shot regardless of his cooperation.
- In a way, Joe Chill was responsible for every event in the Arkham Series, as he unknowingly and indirectly created Batman.
- It is unknown what happened to Joe Chill as he has seemed to disappear after killing the Waynes.
- Nobody but the players knows the identity of the Wayne's killer.
- Batman has most likely been searching for his parent's killer ever since he donned the cowl. But it seems as though he has had no success.
- Joe Chill was referenced in the achievement for the remastered Crime Alley challenge map in Arkham Knight, as the achievement is called "The Chill in the Air".