A Mobile QA (Quality Assurance) developer is responsible for testing mobile applications to ensure functionality, performance, and security. They create and execute test cases, identify and report bugs, and work with development teams to fix issues. They also validate that the application is user-friendly and meets specified requirements. Additionally, they may design automated tests to improve efficiency. The role requires a thorough understanding of different mobile platforms (iOS, Android) and testing tools. QA developers play a vital role in the software development lifecycle, ensuring the final product is free from defects and provides a seamless user experience.