An Avro developer works with Apache Avro, a data serialization system designed to facilitate big data processing and storage. They create, manage, and maintain Avro schemas to define the structure of data for efficient serialization and deserialization. They also implement Avro protocols for data exchange between systems and services. They work on optimizing data storage and processing with Avro, ensuring its compatibility with various languages. Additionally, they handle data encoding and decoding with Avro and work closely with other developers to integrate Avro into big data solutions. Their work is crucial in managing and optimizing big data workflows.