The People
The "People" are the citizens of a nation-state. They come from the Third Estate of the French Revolution—they are the people who work. They form the body politic and are the ultimate source of authority in the functioning nation-state. They are often mistaken for the Mob or the Masses, both of which are degenerations of the People. In the mid-19th century, the People get split into classes, allowing for the Mob and the Masses to make their appearance.
The Mob
The Mob consists of the refuse of all classes of society. According to Arendt, they search for a strong-man or great leader to follow. They always use extra-parliamentary (and often violent) means to accomplish political goals since they are not represented by parties that are based on the classes they have been ejected from. The Mob was harnessed by the elite in the Dreyfus Affair to further antisemitic goals. The Mob also plays a role in imperialism, allying with capital in the case of the pan-movements and the Boers in South Africa.
The Masses
The Masses refers to the mass of isolated, atomized individuals that is created by the destruction of the nation-state and the accumulation of capital during imperialism. The Masses are not the same as the Mob. While the Mob is the refuse of all classes, the Masses are created by the apparent liquidation of classes. The Masses are the basis of totalitarian movements, which rely on a mass of humans who have lost all relations to their fellow man.
The Totalitarian Leader
The Totalitarian Leader is typified by Hitler and Stalin. The will of the Totalitarian Leader is the supreme law in a totalitarian regime, and all those who carry out this "supreme law" view themselves as merely instruments of the Leader's will and ideology rather than autonomous individuals making choices. The Totalitarian Leader is incredibly famous and charismatic, but will be forgotten immediately when he dies. Furthermore, he is the source of the "infallible predictions" so characteristic of totalitarian propaganda.