A Back-End Developer is a type of software engineer who focuses on the server side of web applications. They are responsible for managing databases, server logic, and application programming interfaces (APIs). Their work ensures that the front-end, which users interact with, can communicate effectively with the server and retrieve the necessary data. Back-End Developers typically use programming languages such as Python, Java, or Ruby to build the server-side components. They also work with databases like MySQL or MongoDB to store and manage data. Their role is crucial for the functionality and performance of web applications.