In pre-production, Jim Dear was known as Jim Brown, and Darling was named Elizabeth. These were dropped to highlight Lady's point of view. In a very early version, published as a short story in a 1944 Disney children's anthology, Lady refers to them as "Mister" and "Missis." To maintain a dog's perspective, Darling and Jim's faces are rarely shown. The background artists made models of the interiors of Jim Dear and Darling's house and shot photos and film at a low perspective as a reference to maintain a dog's view.
The film's opening sequence, in which Darling unwraps a hat box on Christmas morning and finds Lady inside, is based upon an actual incident in Walt Disney's life when he presented his wife Lily with a Chow puppy as a gift in a hat box.
Jim Dear and Darling are very loving people, to both to each other and their pets. At first, Jim Dear attempts to be firm with their new puppy, Lady, but he later gives in and allows Lady to sleep with them after Darling requests it. They appear to be dog-lovers, having adopted two dogs: Tramp and Angel, besides having Lady and Lady and Tramp's puppies.
In the first film, Jim Dear and Darling are introduced as a young married couple. At Christmastime, Jim Dear presents Darling with the gift of a cocker spaniel puppy, whom Darling names Lady. That night, they make a bed in the laundry room for Lady, but Lady becomes lonely. Darling wishes for Lady to sleep with them, but Jim Dear remains firm. He finally gives in, though he states that it is just for that night.
A few months later, when Lady is six months old, it is revealed that Lady now sleeps with Jim Dear and Darling regularly. Realizing that Lady has grown up, they present her with a collar and license. Later on, it is shown that they have been unintentionally been treating Lady somewhat coldly. However, Lady soon learns that Darling is expecting a baby. After the baby is born, Jim Dear and Darling introduce Lady to the baby. Soon after, they leave for a short trip, leaving Lady and the baby in the care of Aunt Sarah.
They return near the end of the film. Aunt Sarah reveals that a stray dog had been in the baby's room, and that she had him taken to the pound. After hearing Lady barking, they release her from the basement, where Aunt Sarah had locked her up. Jim Dear realizes that Lady is attempting to tell them something, and so he, Darling, and Aunt Sarah followed Lady to the baby's room. There, Jim Dear, Darling, and Aunt Sarah are able to find a dead rat. They realize that Tramp had been trying to protect the baby from the rat.
Darling, along with Jim Dear and Lady, follows the dog catcher and retrieves Tramp. She and Jim Dear adopt Tramp, and the following Christmas reveals that Lady and Tramp have a litter of four puppies.
Jim Dear and Darling reappear as the owners of Lady, Tramp, and their puppies. Their baby son is revealed to be named Jim Jr. After one of the puppies, Scamp, makes a mess in the house, they are forced to chain the puppy to a dog house outside. Later on, they take the dogs out on a family picnic, during which Scamp steals a chicken to take to the Junkyard Dogs. At the end of the film, Jim Dear and Darling adopt Scamp's girlfriend, Angel, whom he had met on the streets.