A jQuery UI developer is responsible for implementing interactive features on websites using jQuery UI, a set of user interface interactions, effects, widgets, and themes. They work on enhancing user experience by designing and integrating front-end elements. Their tasks include creating dynamic user interfaces, debugging and fixing issues, optimizing web pages for maximum speed and scalability, and ensuring website compatibility across different browsers. They collaborate with back-end developers and web designers to improve usability, assist in developing software documentation, and maintain the standards of web development. They also stay updated with emerging technologies for continuous improvement.