What are people who represent interest groups to legislators called?

The answer to your question is the lobbyists. They are the people who represent interest groups to legislators. The lobbyist's role is to try to influence a government official's decision specifically legislators or the members of the regulatory agencies.

Americans often speak of their country as one of several large regions.  these regions are cultural units rather than governmental units --  formed by history and geography and shaped by the economics, literature and folkways that all the parts of a region share. what makes one region different from another? a region's multicultural heritage as well as distinct demographic characteristics like age and occupation make regions different and special. within several regions, language is used differently and there are strong dialects. there are also differences in outlook and attitude based on geography.