A Hadoop/Spark developer designs, develops, and implements big data applications using Apache Hadoop and Spark frameworks. They handle the processing and analysis of vast data sets, ensuring data's optimal performance, reliability, and scalability. They develop data processing algorithms, create data models, and perform ETL operations. They work on data distribution, security, and storage, often creating Hadoop clusters. They also perform debugging, monitoring, and performance tuning. The developer ensures code quality and often collaborates with data scientists and architects to understand data needs and deliver systems that meet these requirements. They also stay updated with new technologies and advancements.