The Roman orator, lawyer, politician, and philosopher who served as consul in 63 BCE, wrote the foundational Latin works on rhetoric, political philosophy, and moral philosophy, and was executed in 43 BCE on Mark Antony's orders — leaving a body of work that was rediscovered in the 14th century by Petrarch and became the intellectual foundation of Renaissance humanism, early modern republicanism, and the Western rhetorical tradition.
Cicero invented almost nothing. He was a transmitter — translating Greek philosophy into Latin, adapting Greek rhetoric for Roman courts, synthesizing Stoic, Academic, and Peripatetic thought into accessible Latin prose. He was explicit about this: he called himself a philosophical apprentice borrowing from the Greeks. And yet the Western intellectual tradition owes him an extraordinary debt, because the Greek originals he transmitted were often lost and what survived was Cicero's Latin version. When Petrarch discovered Cicero's letters in Verona in 1345 and the Renaissance began, it began with Cicero's Latin. The transmitter became the source.