In practice, many web developers will have basic interdisciplinary skills / roles!
A web developer is a programmer who specializes in, or is specifically engaged in, the development of World Wide Web applications, or applications that are run over HTTP from a web server to a web browser.
Graphic design / web design
Graphic design is the process of visual communication and problem-solving using one or more of typography, photography, and illustration. The field is considered a subset of visual communication and communication design, but sometimes the term "graphic design" is used synonymously.
Information architecture and web usability and search engine optimization in mind
A website's (or intranet's) information architecture has two main components: identification and definition of site content and functionality. the underlying organization, structure and nomenclature that define the relationships between a site's content/functionality.
A responsive website automatically changes to fit the device you're reading it on. Typically there have been four general screen sizes that responsive design has been aimed at: the widescreen desktop monitor, the smaller desktop (or laptop), the tablet and the mobile phone.