A Hogan.js developer uses Hogan.js, a JavaScript templating engine developed by Twitter, to efficiently create web pages that can be rendered on the server-side or client-side. Their responsibilities include writing templates in a mustache-compatible format, compiling these templates into JavaScript, and then rendering these templates with data. They work with JSON data, manage caching, and handle lambdas or higher-order sections. They also ensure that the templates are compatible across different browsers and platforms. Additionally, they may be involved in debugging, testing, and maintaining the templates, as well as integrating them with other front-end and back-end technologies.