Ryan Dahl is a software engineer best known for creating Node.js, a popular open-source runtime environment that allows developers to run JavaScript on the server side. He introduced Node.js in 2009, which has since become a fundamental tool for building scalable web applications. In addition to Node.js, Ryan Dahl has worked on various other projects and technologies. He is also known for his contributions to the JavaScript community and has been involved in discussions about improving the language and its ecosystem. His work has significantly influenced modern web development practices.