Bruce Wayne once said that Rossum had taught him everything he knew about electronics, suggesting that Rossum was once a mentor to the young businessman. He also briefly served as one of theme park tycoon Grant Walker's "Visioneers".
Rossum went into semi-retirement after his daughter was killed in a car accident. In his grief, Rossum thought of making a "perfect" world populated by androids instead of humans, where such things would never happen. To that end, Rossum resumed active leadership of Cybertron and designed and built H.A.R.D.A.C., a prototype artificial intelligence capable of producing androids that could impersonate living people.
Midway through his scheme's execution, Rossum realized that what he was doing was wrong, and that H.A.R.D.A.C. had gone beyond his control. He tried to shut H.A.R.D.A.C. down, but was incapacitated and imprisoned along with James Gordon, Hamilton Hill, and Harvey Bullock. They were rescued by Batman and Barbara Gordon, and he helped them all to escape Cybertron's building before an explosion that destroyed H.A.R.D.A.C. Outside, Hill assured him that he would not be held responsible for his creation's actions.
Rossum retired to a farm outside Gotham, settling for a more pastoral life, though still attended by a host of his robotic creations.
Unfortunately, his past came back to haunt him when a barely functioning H.A.R.D.A.C. managed to create a Batman duplicate. Although he ultimately survived, Rossum's greenhouse was destroyed in the fight between Batman and his duplicate.
Batman later tracked Rossum down when he suspected his involvement in Mr. Freeze's breakout. Rossum denied any involvement, but he did recognize the robot that took Freeze as being of a similar design to one he supplied to his former boss, Grant Walker.
Abilities and Appearance
Rossum was a brilliant inventor and electronics engineer, with a particular fondness for robots designed for various purposes.
He wore old-fashioned clothes, including a bow-tie, and spoke with a Mid-Western accent, giving him a rustic, "hayseed" appearance that belied his vast technological expertise.
The name "Rossum" is a reference to the titular character in the 1921 play Rossum's Universal Robots by Karel Čapek, who coined the term "robot" in this play. The character also has allusions to the character J.F. Sebastian from the film Blade Runner, also played by William Sanderson, who was a retired Replicant (robot) designer who, by the time he shows up in the story, simply makes robotic toy friends for himself. Some viewers had wondered if the name was a version of "Carl Grissom", a mob boss in the 1989 live action film Batman who was the old boss to the Joker, as his true name of "Jack Napier" first appeared in the film and was later used in the animated series. However, it was confirmed by the DCAU Rossum's character was named after the 1921 play, and it was entirely coincidental that the character from the 1989 film had a similar sounding name.