In a major biography of Blaise Pascal, James Connor explores both the intellectual giant whose theory of probability paved the way for modernity and the devout religious mystic who dared apply probability to faith. A child prodigy, Pascal made essential additions to Descartes's work at age sixteen. By age nineteen, he had invented the world's first mechanical calculator. But despite his immense contributions to modern science and mathematical thinking, it is Pascal's wager with God that set him apart from his peers as a man fully engaged with both religious and scientific pursuits. One night in 1654, Pascal had a visit from God, a mystical experience that changed his life. Struggling to explain God's existence to others, Pascal dared to apply his mathematical work to religious faith, playing dice with divinity: he argued for the existence of God, basing his position not on rigorous logical principles as did Aquinas or Anselm of Canterbury, but on outcomes—his famous wager. By applying to the existence of God the same rules that governed the existence and position of the universe itself, Pascal sounded the death knell for medieval "certainties" and paved the way for modern thinking.