Some people are good at fighting. Some are good at thinking. Some have special powers. And some... have just the right info to make everyone else useful. This is the person who always seems to have the dirt on everybody. The person who runs an information-gathering system, with a network of informers. If the contact is a recurring character and the Knowledge Broker and the protagonist are different genders (or not), expect romantic subtext. Real Life information brokers tend to be consultants who work in market research, though there are exceptions. See also The Fixer.