A Data Marts developer primarily designs, develops, and maintains data marts - subsets of data warehouses. They extract, transform, and load (ETL) data from various sources into the data mart. They also create and manage data models, schemas, and data dictionaries, ensuring the data is organized and accessible for data analysis. They work closely with data analysts and business stakeholders to understand their data requirements and provide tailored data solutions. Their role also involves ensuring data quality and integrity, troubleshooting data-related issues, and optimizing data retrieval performance. Additionally, they may also need to document and implement data governance policies.