"On or about December 1910, human character changed."
— Virginia Woolf, 1924

She was exaggerating — but only a little. Woolf saw a fundamental shift in human relations taking place at the beginning of the 20th century "between masters and servants, husbands and wives, parents and children." Those changes, she predicted, would bring about transformations in every sphere of life, from religion to politics to human behavior. Few would say she got it wrong.

A century later, we are living through another transition. The way we connect with one another and with the institutions in our lives is evolving. There is an erosion of trust in authority, a decentralizing of power and at the same time, perhaps, a greater faith in one another. Our sense of identity is more variable, while our sense of privacy is expanding. What was once considered intimate is now shared among millions with a keystroke.

More than anyone else on the world stage, Facebook's Mark Zuckerberg is at the center of these changes. Born in 1984, the same year the Macintosh computer was launched, he is both a product of his generation and an architect of it. The social-networking platform he invented is closing in on 600 million users. In a single day, about a billion new pieces of content are posted on Facebook. It is the connective tissue for nearly a tenth of the planet. Facebook is now the third largest country on earth and surely has more information about its citizens than any government does. Zuckerberg, a Harvard dropout, is its T-shirt-wearing head of state. (See portraits of TIME's 2010 Person of the Year: Mark Zuckerberg.)