A Media Queries developer is responsible for creating responsive web designs that adapt to different devices, such as smartphones, tablets, and desktops. They write media query code, a type of CSS technique, to adjust the website's layout, images, and other design elements based on various parameters like screen resolution, orientation, and aspect ratio. Their goal is to ensure optimal user experience across all platforms by making sure the website is aesthetically pleasing and functional regardless of the device it is viewed on. They often work closely with web designers and developers to integrate responsive design into the overall website development process.