A Marvel App developer designs, constructs, tests, and maintains applications using the Marvel API. They incorporate Marvel's vast database of comics, stories, and characters into engaging and interactive applications. They handle the integration of front-end elements, ensure high performance and responsiveness to requests, and build reusable code and libraries for future use. Tasks also include optimizing the application for maximum speed and scalability, implementing security and data protection, and designing and implementing data storage solutions. They work closely with UI/UX designers to ensure a seamless user experience. They also troubleshoot, debug and upgrade the app regularly.