Oligarchs are the level above politicians. You can think about them as the true employers of most politicians. (If I can make an analogy, for a politician the voters are merely a problem to be solved; the oligarch is the person who gave them the job to solve the problem.) Imagine someone who has incredible wealth, owns a lot of press in the country, and is friendly with many important people in police, secret service, et cetera. The person who, if they like you as a wannabe politician, can give you a lot of money and media power to boost your career, in return for some important decisions when you get into the government.