Adam Hendricks is a guard at Arkham Asylum
Adam Hendricks was abused as a young boy by his father and imagined that marbles were little worlds and universes he could escape too. He eventually became a guard an Arkham Asylum and talked with Dr. Harleen Quinzel about the trauma he faced as a child. He never told another soul. Unfortunately, for him his trust was betrayed years later when Harley Quinn (also known as Harleen Quinzel) used his love of marbles to distract and kill him at his post in Guard Tower Three. She did this in her attempt to break into Arkham and kill the Joker. The fact that Harley liked him and considered him one of the "good ones" didn't enter into it.