A Hadoop developer designs, develops, installs, configures, and maintains the Hadoop application. Their role involves programming in Java, Python, and SQL, and handling large datasets using Hadoop ecosystem components like HDFS, MapReduce, Hive, and HBase. They manage data processing and analysis, ensuring efficient data loading, transformation, and storage. They also perform troubleshooting, debugging, and upgrading of the Hadoop clusters. Additionally, they ensure system's security and privacy, and may work on data modelling, ETL development, and data warehousing. Essentially, they enable businesses to make sense of big data, providing insights for data-driven decision making.