A CodeIgniter developer is responsible for creating and implementing an array of web-based products using PHP, MySQL, Ajax, and JavaScript. They develop back-end components, connect the application with other web services, and assist front-end developers by ensuring their work integrates with the application. They also utilize CodeIgniter, a powerful PHP framework with a small footprint, to build full-featured web applications. The developer ensures the performance, quality, and responsiveness of applications. They also identify and correct bottlenecks, fix bugs, and maintain code quality. Their role is integral in developing, releasing, and maintaining software applications according to business needs.