Dr. Caulder, also known as the Chief, is an experimental doctor.
Caulder rescued Rita Farr from an institution, saved Cliff's brain after a car accident, and in 2016 cured Gar Logan of a rare disease in the Congo. By 2018, Caulder lived in a house in Covington, Ohio with the three, as well as Larry, where he performed scientific experiments in the hopes of bettering medicine. At some point, he'd lost the ability to walk, but soon learnt again.
Leaving to retrieve the dying body of Shyleen Lao, Caulder returned, surprised to find Rachel Roth in his house. Before anything, his adopted family assisted Caulder in stabilizing Shyleen, as she'd been in an accident and her body was freezing. Rachel intervened, helping to calm Shyleen down and allow an injection of Caulder's to work. Following this, Caulder scolded Gar for having brought Rachel into their secret circle, but reminded him that he cared for him. They all joined together for tea, where Dr. Caulder explained to Rachel who they were, that he'd helped all of his subjects to live again after various accidents. Hoping to help Rachel, she was put on to a medical table and strapped down. Deciding to back out of the experiment, Rachel pleaded to be let go, but Gar's attempts were stopped by Caulder. Rachel ultimately broke free, using darkness to pick up and throw around the doctor, breaking his back once more.
- Expert scientist: Caulder possesses an incredible scientific knowledge, being able to save Cliff's brain after a horrific accident, transferring it into a robot body, as well as saving Gar Logan from an otherwise rare disease.