Why was John Locke regarded as the father of classical liberalism?

Classical liberalism is the set of ideas most identified (within the United States at least) as "libertarianism." Classical liberalism formed in opposition to hereditary monarchy, particularly monarchy's absolutist variant.
Locke, writing in the late seventeenth century, articulated many of the ideas held dear by classical liberals. One was that every human being had certain rights that could not be taken away by a government without one's consent. This was because the government did not grant people these rights in the first place. They were rather "natural rights," that is, they were inseparable from the human condition. So government by the consent of the governed was a fundamental belief of classical liberalism, and it followed that government should be as unobtrusive as possible into the lives of the people who gave it permission to govern. Taxes should be very low, government interference in the economy should be minimal (so as not to deprive people of their property rights), and government should be, as much as possible, a reflection of the will of the people—or at least those with property. Classical liberals also, like Locke, supported civil liberties like freedom of religion, due process in the courts, free press, and other institutions we would associate with modern liberal democracies. Locke's On Toleration was a touchstone for religious tolerance, and he generally favored the free press. So for these reasons, Locke is considered the founder of classical liberalism.