A Middleware-ESB developer designs, develops, and maintains the Enterprise Service Bus (ESB) system, which facilitates communication between different software applications. They create integration solutions, ensuring seamless data exchange between disparate systems. They analyze business requirements, design and implement middleware tools, and troubleshoot any issues. They are also responsible for monitoring system performance, identifying bottlenecks, and optimizing workflows. Furthermore, they document system design and operations, and may provide training to other team members. They need a deep understanding of ESB technologies, API management, and programming languages like Java or .NET.