Most of the villains St. Canard gets to suffer are, in theory, simple dealings. You trick or overpower them and then lock them away for life in a highly secure penitentiary. Not so much for the hyper-destructive powerhouse Cat-Tankerous, who out of his suit is a little boy of about ten years of age: Mortimer L. Marquand. How do you handle that? With thousands of hours of community service and fingers crossed. Despite Mortimer's return to civilian life, the sentiments that made him into a criminal remain. He is fascinated by his adult colleagues and follows their exploits with glee.
Prior to receiving the suit, Mortimer L. Marquand was just an ordinary school-age boy with a deep but unrequited crush on his schoolmate Gosalyn. Inspired by the sight of her as "Gosmoduck" during the events of "Crisis on Infinite Darkwings", Mortimer attempted to build his own Gizmo Suit and impress her, but to no avail. He then receives the Cat-Tankerous suit, an enormous suit of indestructible armor, with a note saying for him to "be a better man", driving him into a single-minded obsession towards destroying St. Canard and Darkwing Duck. On February 4th, 2015 Joe Books released "The Definitively Dangerous Edition"; in this version, Mortimer does not have a crush on Gosalyn but admires her strength when she saves him from bullies mocking him for his comic book collecting. He still attempts to build his own Gizmo suit, but when he receives the Cat-Tankerous suit, the note reads "Show them who you really are." He is eventually defeated by Darkwing when distracted by Gosalyn, scolding him for becoming a bully himself.
- Despite the similarities between Cat-Tankerous and Fluffy, the latter did not inspire the former's creation. Cat-Tankerous is instead modeled after the Juggernaut from X-Men and Rhino from The Amazing Spider-Man.
- According to Aaron Sparrow, "Originally Ian's version of Cat-Tankerous was supposed to be an ordinary female housecat that became intelligent, but James felt it didn't work in the script he was given, so he and Chris Burns reworked it. I wonder if part of the reason was because it was too close to Fluffy's origin.