A DDMS (Dalvik Debug Monitor Server) developer is responsible for debugging and monitoring applications in the Android platform. They use the DDMS tool to track memory usage, thread activity, and network traffic, to manage port-forwarding services, to simulate incoming calls and SMS, and to set breakpoints. They can also capture screenshots of the user interface, inspect the heap, and view detailed log files. The DDMS tool allows developers to identify and fix performance issues, understand application behavior on different Android devices, and enhance the overall quality of their applications. It's an essential part of Android app development.