A Fluent NHibernate developer designs, develops, and manages databases using the Fluent NHibernate Object-Relational Mapping (ORM) tool. They create mappings between the .NET object domain model and the relational database to simplify data access. Their tasks include setting up Fluent NHibernate configuration, writing mapping classes, and using Fluent NHibernate's querying API. They also work on data conversion, performance tuning, and troubleshooting. Fluent NHibernate developers often collaborate with other developers and stakeholders to ensure the database structure meets the needs of the application, and to maintain data integrity and security. They also document their work for future reference.