It is a fairly common trope to have a "master spy" who feeds information to people. She or he gathers this information from an unspecified army of "birds" or "sparrows" or "eyes-and-ears" or whatever label the specific source cares to name it. The details change across genres and sources. But the trope remains: This unassuming person has connections with some vast network of people, all of whom feed him/her their juice gossip.
But in each, this master spy is an established character, already at the center of their web of connections and sources.
How did they build that network? How does one go from being a normal person to having that vast network of sources?
Are there real-world people who have done this? Or is it a purely fictional trope? (I don't mean CIA or KGB agents who have a few sources that they work over years, but the fiction trope of the true master of spies, knowing almost everything and everyone...)