Ted Wiggins, an idealistic 12-year-old boy, lives in "Thneedville", a walled city that, Aside from the citizens, is completely artificial. They sets out to find the one thing that will win Ted's affection of Audrey, the girl of his dreams, who wishes to see a real tree. There's energetic grandmother suggests the boys speak with the Once-ler on the matter, and the boys discovers that their city has been closed off from the outside world, which is a contaminated and empty wasteland. The Once-ler agrees to tell Ted about the trees if he listens to his story over multiple visits. Ted agrees, even after the mayor of Thneedville, Mr. O'Hare, the greedy proprietor of a bottled oxygen company, confronts the boy and pressures him to stay in town.
Over the visits, the Once-ler recounts the story of how he met the Lorax, a grumpy yet charming creature who serves as guardian of the land he arrived in and actively resists his logging until the Once-ler agrees to desist. When the young businessman introduces a revolutionary invention from the native Truffula Tree's tufts, the thneed, it eventually becomes a major success and the Once-ler's family is brought in to participate in the business. Keeping his promise at first, Once-ler continues thneed production by harvesting the tufts themselves in a sustainable manner. Unfortunately, his greedy and lazy relatives convinced him to resume logging as a more efficient gathering method, and the destruction of the forest spirals into a mass overproduction. Flush with wealth, the Once-ler rationalized his short sighted greed into an arrogant self-righteousness that even co-opts the helpless protests of the Lorax for his own ends.