In his first appearance, he is shown to be very grumpy and angry, as if mad about being kept as a pet, and doesn't believe the Master (Rob) is wonderful. This is possibly because of his past experiences with humans who screamed at him, threw things at him, and called the exterminator on him. He's rude to pretty much everyone, but as the film goes on, Ratso's heart begins to warm up to the others, especially when Radio sacrifices his rare cathode tube to give old Wittgenstein the spark he needs to help them save the animals from being shipped to Tartarus Laboratories. Once the gang manages to reach the truck, Ratso pulls Maisie out from under some boxes and mourns over her, believing her to be dead. However, she then wakes up and calls Ratso a hero, to which he responds by blushing good-naturedly while holding his tail.
The next morning, Maisie allows Ratso to be the first thing for her babies to see, and he is happy to play with the kittens after they tackle Ratso and lick him. Later, when Ratso hears that the other animals have homes except him, he sadly sulks. However, he is overjoyed when he hears Chris say that he's coming with them, stating that she "thinks he's kinda cute." Ratso is also happy when the couple revive Radio with a replacement cathode tube. In the end, Ratso leaves for his new home with Toaster and his friends, while waving goodbye to the other animals and singing, "Hang In There, Kid."
In his second appearance, he is shown to be very kind and helpful to Toaster and the other appliances. He stays behind and stands watch by keeping the baby monitor from going off, while Toaster and his friends go on a mission to rescue Robbie, who is referred to as the "Little Master" by the appliances.
- Ratso bears some resemblance to The Rat from Lady and the Tramp, but unlike Ratso, he's an antagonist.
- He is the first Disney rat character who is a protagonist, the second being Remy from Ratatouille.
Songs: April Showers | Tutti Frutti | City of Light | Mammy | It's a 'B' Movie | Cutting Edge | Worthless | Bread and Butter | I See a New You | Floating | Fight Right | Home Again | I'm Into Something Good | Remember That Day | Cocktails for Two | Super Highway | Chomp and Munch | Hang In There, Kid