An AWS ElastiCache developer works with Amazon's web service that simplifies and automates tasks related to deploying, operating, and scaling an in-memory cache in the cloud. They are responsible for improving application performance by storing critical pieces of data in memory for low-latency access. Their tasks include managing caching strategies, configuring the ElastiCache environment, and optimizing cache utilization. They also troubleshoot performance issues and ensure data security. The developer needs to understand the application's requirements and data access patterns to effectively implement ElastiCache solutions, thus enhancing the application's responsiveness.