A Graphviz (DOT) developer is primarily responsible for creating visual representations of abstract data structures and relations. They use Graphviz, a graph visualization software, and its language, DOT, to design and implement graph descriptions, which can depict data structures like networks, workflows, or hierarchies. Their tasks involve designing nodes, edges, and properties of graphs, setting up graph attributes like colors, fonts, node shapes, and managing the layout of the graph. They also debug and optimize these visualizations for performance and readability. Furthermore, they often integrate these graphs into software applications or web pages.