A Grand Central Dispatch (GCD) developer designs and implements software applications using Apple's GCD technology. GCD is a concurrency and parallelism library that allows efficient execution of tasks in iOS and MacOS. The developer's responsibilities include creating multithreaded code, managing queues and tasks, handling asynchronous events, and optimizing application performance. They ensure efficient use of system resources, minimizing latency and increasing responsiveness. They also troubleshoot and resolve issues related to GCD, and collaborate with other team members to integrate GCD into larger projects. They need a strong understanding of computer science concepts like multithreading and concurrency.