A Guava libraries developer is responsible for implementing and managing Google's open-source Java libraries, known as Guava. Their tasks include creating data structures, implementing caching, concurrency, and other utilities to enhance Java's functionality. They also ensure the libraries' compatibility with Java's core libraries. Additionally, they handle issues such as memory leaks and manage common programming tasks to improve code readability and efficiency. They also collaborate with other developers, providing them with tools to write better Java code. Furthermore, they continuously update and optimize the libraries to keep up with evolving technology trends.