A Mahout developer specializes in creating scalable machine learning algorithms using Apache Mahout, an open-source project. They handle large data sets, often in a big data environment, and use Mahout's pre-built algorithms for classification, clustering, and collaborative filtering to analyze data and uncover insights. They also customize and develop new algorithms as per specific requirements. A Mahout developer's tasks include data preprocessing, implementing machine learning techniques, creating predictive models, and integrating these models into existing systems. They must also troubleshoot and optimize these algorithms for performance and reliability.