Cruella first meets Lars when she stumbles into an art house show. Lars' main style of art is shown to be black spots on a white surface, similar to that of a Dalmatian's coat. Lars is attracted to how Cruella is able to see his artistic vision, and agrees to do a painting for her in exchange for her being his muse.
On his first painting for her, Cruella comments it's all wrong, despite his claim for it to be his best work yet. Cruella notes it needs to be better than his best, and after being seduced by Cruella, Lars vows to paint another canvas, one after another, until he has found artistic perfection and won't stop until Cruella is pleased.
Many failed attempts later, he submits in defeat about not being able to please Cruella, but she assures him that all he needs is some inspiration. She later returns with the captured Dalmatian puppies, Lars then bursts out with joy and delight, hugging the puppies, believing that Cruella wants him to paint a portrait of them, when in fact she wants him to make art with the puppies (use their coats as canvas, etc.).
Lars turns her down, commenting how he may be eccentric but is not a sicko, and says she will not harm any of the puppies if he has anything to say about it. Cruella then gags him and ties him up and calls Lars a disappointment, but figures if she can't have a portrait, at least she can get a coat.
In the credits, it is shown he soon gets labeled as an artistic genius for a piece of art that the pups actually made when being chased by Horace and Jasper.
While Lars does appear in the Patch's London Adventure video game, he is shown here as an enemy who will attack Patch in the studio levels. This is despite the fact that, in the film, Lars refuses to let any harm come to the Dalmatians and also helps Patch against Cruella. He uses his paintbrush as a weapon in the game.