Mark Zuckerberg has become the single most powerful person in political advertising through his company, Facebook. Millions turn to Facebook every day to find out what is going on in the world, far more than use any other news medium, including television and newspapers.
Facebook, which started as a platform to facilitate hookups for students at Harvard, has evolved first to a tool used by thousands to keep up with friends and eventually to become the primary purveyor of news both accurate and inaccurate.
Facebook has become fantastically profitable by helping advertisers target their messages directly at the users most likely to buy their products. Political campaigns soon took notice, paying to direct their messages to the voters that they want to reach and influence.