A custom controls developer designs, creates, and maintains customized controls for software applications. They work closely with software developers and engineers to understand the specific requirements of a project and then develop controls that enhance functionality and user experience. This can include creating unique buttons, sliders, or other interactive elements. They need to have a strong understanding of programming languages, user interface (UI) design, and user experience (UX) principles. They also test the controls for any bugs or issues and make necessary modifications to ensure optimal performance. They play a crucial role in making software applications more user-friendly and efficient.