A grown baby mainly called, with his mob mentality and his cigar, he is the right baby for the job. Baby Herman has a deep voice and rides in a stroller. He wears a pink bow and diapers. His stage persona, a baby always getting into mischief, is reminiscent of two Tom and Jerry cartoons where the two would have to work together to keep a baby out of trouble; Busy Buddies (1956) and Tot Watchers (1958).
Baby Herman is very impatient and irritable, as shown when Roger messes up during their act at the beginning of the movie. Despite this, he cares about Roger and considers him a good friend. Baby Herman also claims that Roger is innocent when he is framed for the death of Marvin Acme.
In the cartoons, he is depicted as a baby who wanders off and always gets Roger into trouble. Off-set, he reveals that he is really a middle-aged man with a gravely voice who only looks like a baby. He constantly smokes and hits on women. He tells Eddie later in the film that Roger would never commit murder and that he has been framed in Marvin Acme's death and gives him a few clues to support this. At the end of the movie, he celebrates with the other Toons after Judge Doom is defeated and Toontown is awarded custody of the Toons in Marvin Acme's will.
Events start with Baby Herman and Roger rehearsing their latest Toon short for Maroon Cartoons, "Something's Cooking", but Roger ends up ruining the take for the 23rd time because he can't produce the result that is written in the script, frustrating his co-star, forcing him to retire to his trailer for a nap.
At some point, Baby Herman learns of Roger being wanted by police due to being the prime suspect in the murder of Marvin Acme, owner of Toontown and CEO of the Acme Corporation.
Some time later, Baby Herman is outside the office of Valiant & Valiant Private Investigators when Eddie Valiant returns and discovers him when he notices Baby Herman's handler lighting up his cigar. After Baby Herman "encourages" his handler to head downstairs to pick up something for him, leaving him alone with Valiant, Herman tries to convince Valiant that Roger is innocent of murdering Acme, citing his long-time relationship with Roger as friends and co-workers as incentive to his belief Roger is being framed for the murder. He then produces a newspaper with the headline mentioning that Acme left no will behind regarding Toontown's future should anything happen to him. Herman knows that Acme promised to entrust Toontown to the Toons in his will, and gave his solid oath that he would upon his death. Valiant has a hard time believing it due to Acme's history as a prankster, and thinks Herman and the rest of the Toons are being duped. However, Herman argues that since it was Valiant's fault that got Roger into trouble with Judge Doom, it should be Valiant who gets him out of it.
Unfortunately, when Herman offers to pay Valiant for helping Roger, this sets off Valiant's hatred of Toons because of his brother's death by a Toon, and he tells Herman off before shoving Herman's pram towards the stairs, where it collides with his handler just coming back up the stairs, and causes Herman's cigar to fall out of his hand and onto the floor. Herman can only look down at it before bursting into tears like a baby, while Eddie smugly enters his office. However, Eddie soon discovers that Baby Herman was right when he sees Acme's will in his pocket in one of the photographs he took of Acme and Jessica Rabbit playing pattycake in her dressing room at the Ink and Paint Club, but after some thought, decides it is not worth it, until he finds Roger sleeping in his bed, hiding from the Toon Patrol.
Baby Herman reappears after Eddie stopped Judge Doom's plan to destroy Toontown for a freeway, once again citing that without Acme's will, Toontown is still vulnerable to another contractor's wrecking ball, before Eddie interrupts to have Roger read his love letter to Jessica, which is soon revealed to be Acme's will, written in Disappearing/Reappearing Ink, thereby entrusting Toontown to the Toons and saving it from further harm. Baby Herman joins the other Toons in singing "Smile Darn Ya Smile" as Eddie, Dolores, Roger, and Jessica head into Toontown with the rest of the Toons right behind them.
Baby Herman is a regular in the Roger Rabbit and Roger Rabbit's Toontown comic books.
Baby Herman can be seen reading a paper in the queue for Roger Rabbit's Car Toon Spin.