A JRuby developer is a valuable asset due to their proficiency in both Ruby and Java. They can develop high-performance, scalable applications, and offer seamless integration with Java codebase. This allows for leveraging Java libraries and frameworks, enhancing functionality and efficiency. JRuby developers also have the ability to run Ruby applications on any Java platform, ensuring compatibility and flexibility. Their skills can help streamline development processes, improve code quality, and build robust, secure applications. The strong community support for JRuby also ensures continuous learning and improvement.