A Graph Data Modelling developer designs, implements, and optimizes graph databases. They use graph theory to establish relationships between data points, enhancing data visualization and analysis. They work with data scientists and analysts to identify important data connections and develop algorithms to extract meaningful insights. They maintain the integrity and security of the data, ensuring efficient data retrieval. They also optimize database performance and troubleshoot any issues. Their role involves a mix of data analysis, programming, and system design, with a focus on creating effective data models to support business decisions.