A CoreData developer is responsible for designing, implementing, and managing databases and data storage systems for iOS applications. They use Apple's CoreData framework to create data models, define relationships between data entities, and manage data objects. They also handle data migration, synchronization, and consistency across multiple devices. Moreover, they ensure data integrity, optimize data retrieval, and troubleshoot data-related issues. Their role is crucial in enhancing the performance and user experience of applications by ensuring effective data management. They also collaborate with other developers to integrate CoreData into the overall app architecture.