A Karma Test Runner developer is responsible for managing and executing tests in a development environment. They use Karma, a JavaScript test runner created by the AngularJS team, to automate browser-based testing. Their role includes writing test cases, integrating Karma into development workflows, and ensuring the compatibility of code across different browsers and platforms. They troubleshoot and fix failures in automated tests, helping to maintain high code quality. They also collaborate with other developers to ensure code changes don't break existing functionalities. Their ultimate goal is to facilitate efficient testing processes and contribute to the creation of robust software applications.