A Cross-Origin Resource Sharing (CORS) developer is responsible for implementing CORS policies on web applications to enable secure cross-origin requests. They manage how resources are shared between different origins, defining which domains can access data from a web server. They work on configuring server-side settings to allow or deny specific types of cross-origin requests, such as GET, POST, or PUT. This includes setting HTTP headers to control permissions and prevent security vulnerabilities. Their work is crucial in maintaining the security and integrity of web applications while ensuring a seamless user experience across different domains.