A CMS developer designs, maintains, and improves websites using Content Management Systems like WordPress or Drupal. They create custom themes and plugins, integrate APIs, and ensure the website's functionality aligns with user needs. The developer ensures the CMS is user-friendly, allowing non-technical personnel to update site content. They also focus on SEO optimization, site speed, and mobile responsiveness. Their role includes troubleshooting issues, performing updates and backups, and maintaining the site's security. They often work closely with designers and other developers to implement complex features and maintain a consistent look and feel across the website.