A Big Data Developer is primarily responsible for designing, developing, and maintaining large-scale data processing systems and databases. They work with complex data sets to analyze, interpret, and draw insights that can help businesses make informed decisions. Their tasks include writing complex queries, creating data models, ensuring data accuracy and accessibility, and developing algorithms for data processing. They work with tools like Hadoop, Spark, and NoSQL. In addition, they also handle data security, privacy, and compliance issues. Their expertise helps companies leverage the power of data to drive business growth and innovation.