Arnold was juvenile delinquent in his youth and spent time in the Gotham City railroad tracks with his little brother Michael. Although he was against his brother's actions, Michael saved Arnold from an oncoming train at the price of his leg. This action haunted Stromwell good enough into late adulthood. However, he continued his criminal life and became one of the main mob bosses in Gotham which fulfilled his desire to "own the city" when he grows up.
Batman invaded Arnold's mansion to catch his nephew Tony Zucco who was the suspect of the murder of Dick's parents John and Mary Grayson. After this brawl, Stromwell disowned Zucco as his nephew. Besides this event, there is little known about Arnold's criminal activities except that he sells and makes illegal drugs.
In the episode "It's Never Too Late" (this episode was produced and aired before Robin's Reckoning), he's in a mob war with Rupert Thorne. This brawl between these two bursted when Stromwell's son Joey went missing. Rupert tried to kill Arnold by setting him up in an exploding restauraunt but was saved by Batman. Batman attempted to get Stromwell reformed and turn State's evidence to the police with the help of Michael who is now a priest. There were several other factors that influenced Arnold's decision, one of them which is the effect of the drugs made by him on his son. Stromwell was convinced by Michael in the same railyard the train incident took place. Stromwell decides to do the right thing by telling Commissioner Gordon that he had a statement to make which finally shuts down and exposes the mob group and Arnold moved on from his life of crime.
- He was voiced by Eugene Roche.