A Matplotlib developer creates data visualizations using the Matplotlib library in Python. They collect and analyze data, then transform that data into meaningful, easy-to-understand graphical representations such as bar graphs, scatter plots, histograms, and more. They customize the appearance of these graphics by manipulating various elements like labels, colors, line types, and axes. Additionally, they ensure the visualizations are interactive and dynamic for better user engagement. They also collaborate with data scientists and analysts to understand the data and provide insights. Their work is crucial in conveying complex data in a simplified manner to aid decision-making processes.