A ETL developer is responsible for developing, testing and maintaining Extract-Transform-Load (ETL) processes to support data warehousing activities. They work with business analysts and developers to understand the data requirements of new systems and design ETL processes to load the required data into the system. They also develop tools and scripts to automate the ETL process. In addition, they monitor the ETL process to ensure that it is running smoothly and troubleshoot any issues that may arise.