Role in the film
Dr. Ronald Olsen comes to the twins during a fight between them, offering them a job as volunteers at the Gemini project to make up for Dr. Spaulding kicking Cody out of his internship, to which they accept. He puts them through a series of tests, mostly through electroshock therapy in response to visual identifiers.
Through his research though, he has discovered that the Corsican fruit has a bizarre effect on twins, allowing them to experience each other's feelings and emotions. As part of his experiment, he gives Zack and Cody the fruit, as well as the other members of the Gemini Project.
When Zack and Cody go through his office, they learn that Dr. Olsen in fact is not working in their best interests, and is using the Corsican fruit to create a hive mind of twins, all under his control. Though he is unable to brainwash Zack and Cody, he sends hundreds of other twins to capture them so that his hive mind can be complete, he was revealed to be Donald's evil twin brother who disappeared when the scicetific community threw him out and When he attempts to merge the twins, much to the dismay of Mr. Moseby, Bailey, London, and Woody, they continue to fight and the machines designed to run the project are destroyed which sets free the other twins from its control.
Once Dr. Olsen begins to threaten everyone, Bailey uses a lasso to catch him until the police can arrive to arrest him. the Sapulding twins actullay wanted to be like each other all along and promise to meet after Ronald is released from prison.