houses and princes
The banking house
They control the monetary wealth of the cites, of all the houses they are the most dangerous and willing to do whatever it takes to get their way. The princes despise them because they will blackmail the cites whenever they can. Their preferred method of obtaining power is to loan money to a noble that could never pay it back, and when he cant pay, they take everything from him, including his title, turning the noble into little more than their puppet.