Mr. Simpkins is an antihero, later true main antagonist of Chuggington and the strict minister of chuggers, who examines the Trainees during their passenger carriage tests. He isn't the easiest man to work with as he takes things much too seriously and doesn't take a joke either. It only takes a wise old chugger like Irving to make sure Mr. Simpkins does his job properly and behave nicely.

In "Koko Pulls it Off"

Koko fails her test when she bumps the passenger car after Mr. Simpkins falls down. Mr. Simpkins told her not to take the retake until next year, but this make Koko gallivant off from her test crying when she met Irving. Irving asks Koko if she wants to be recycled but she doesn't want to and she told Irving the whole story. Irving then scolded Simpkins for taking things too far by being mean, and he told him the whole story on how he got his recycling badge. This prompted Simpkins to apologize for his behavior. Simpkins then asks Koko to start the test again and she retook her test. And most of all, Koko did pass. After the tests, Simpkins promises to behave nicely to chuggers from now on.