A Markup developer designs and creates web pages using markup languages like HTML, XML, and XHTML. They structure and present content on the web in a way that's accessible and user-friendly. Their tasks include writing code, debugging, maintaining websites, ensuring cross-browser compatibility, and incorporating multimedia elements like images, audio, or video. They also work closely with other teams like UI/UX designers and back-end developers to ensure seamless integration of all website components. Additionally, they follow SEO best practices and adhere to web standards and accessibility guidelines to ensure optimal website performance.