A Google Cast developer creates applications for Google Cast devices like Chromecast. They utilize Google Cast SDK to develop apps that can send content from a variety of devices to a large display. Key tasks include designing user interfaces, coding and debugging, testing applications, and updating existing apps for compatibility with newer devices or software updates. They also collaborate with other team members, including UX/UI designers and quality assurance testers, to ensure the apps deliver a smooth, high-quality user experience. They need to stay updated with the latest technologies and trends in the Google Cast environment.