Big Brother is not really a character; it is a metaphor for the power that the Party has and for all dictators and despots the world has ever known. The Party in 1984 uses Big Brother to intimidate, to rule, and to inspire loyalty. Posters of Big Brother are everywhere in Oceania. His face is more familiar than any other. The people are told that Big Brother loves them and takes care of them, so that most people love and are fiercely loyal to "him," and thus to the Party. Decisions are made by the Party in the name of Big Brother and because the people love him, the Party is free to establish any laws they want and they have total rule over the land. The many posters tell people that Big Brother is watching them, which in many ways he is. The Party uses two-way telescreens and hidden microphones and cameras to keep watch on people. Because they know they are being watched, people are less likely to do anything they know would displease Big Brother. Also, the people are less likely to defy Big Brother because they fear the retribution.
Although Big Brother is never seen in person, his presence is felt as the supreme leader on TV screens, in pictures, and on coins. Big Brother is the all seeing eye that watches everything that the inhabitants of Oceania do and think. To those who work for the Ministry of Truth, Big Brother is to be worshipped as an idol. He demands love from his people; everyone must revere Big Brother like a god. He also inspires fear and paranoia, the typical response of people who are always being watched. His presence is used to keep people in line.
Big Brother is a symbol of a tyrannical dictator who demands absolute obedience from his people in all aspects of life. When the state controls every aspect of your life, you have no choices or freedoms. You don't even have control over your thoughts.
The Party uses psychological manipulation and the process of Doublethink in order to keep people from having independent thoughts.
big brother is a collective name for their government, they say big brother is watching they mean you are always being watched by the government and anyone against the government shall be put through things like room 101 which contained the persons deepest fears.
He is arguably a figurehead in the book, as there is no definitive appearance of Big Brother in the book. O Brien does not answer as to whether Goldstein, the supposed enemy of the Party, and neither does he suggest or confirm the existence of Big Brother. He looks over the whole of Oceania, as is supposedly the person to look up, to respect.
Big Brother, although not a tangible character is ever present in the story. The concept of "big brother watching" is all that a society of brain washed drones needs to stay in line. Also, the concepts of Ingsoc and the idea of a Big Brother waiting to catch a person in some sort of crime is enough to keep the members of thi society in check.