An Apache Flink developer works on big data processing, designing and implementing scalable data streaming applications. They utilize Apache Flink's capabilities to process large volumes of data in real-time. Their responsibilities include writing, testing, and optimizing complex data processing algorithms, ensuring high performance and reliability. They manage Flink clusters, handle fault tolerance, and maintain data accuracy. Additionally, they collaborate with data scientists and analysts to understand data needs and deliver efficient solutions. They also stay updated with new features and improvements in Apache Flink to enhance application performance and usability. Their role is critical in driving data-driven decision making.