Kernel
Smith's The Theory of Moral Sentiments (1759) and The Wealth of Nations (1776) bracket the philosophical and the economic projects that, taken together, found modern social science. The pin-factory passage in Wealth — division of labor as the engine of productivity — is the single most-cited paragraph in 250 years of economic writing.
Contribution
Division of labor; the "invisible hand" (mentioned three times in his corpus, expanded into civilizational doctrine by his successors); the theory of moral sentiments as the empirical foundation of ethics; the systematic critique of mercantilism that underwrites the 19th-century free-trade order.
Lineage
Edinburgh and Glasgow; close intellectual partnership with David Hume; influenced French Physiocrats via his time in Paris (1764–66). His successors are Ricardo, Mill, Marx (who reads Smith very carefully), Marshall, Keynes — the whole of subsequent political economy is a series of footnotes.
Civilization-scale significance
The figure in whom economic reasoning crosses the threshold from policy advice into a self-conscious discipline. Smith is what makes "the market" thinkable as a system rather than a metaphor.