A full stack developer is a versatile programmer skilled in front-end and back-end development. They handle complete web applications, from designing user interfaces to managing servers and databases. Key responsibilities include developing responsive UIs with HTML, CSS, and JavaScript, creating server-side logic with languages like Node.js or Python, managing databases (SQL and NoSQL), and deploying applications using CI/CD practices. Essential skills encompass proficiency in multiple programming languages, frameworks, version control systems, and cloud services. They are crucial in bridging the gap between front-end and back-end, ensuring seamless integration and functionality of web applications.