Gottfried Leibniz (1646-1716): German rationalist philosopher who taught that reality is composed of monads—simple substances that have no spatial extension. God is the supreme monad and creates and conserves all other monads. Monads do not really interact with each other but appear to do so due to the "pre-established harmony" that God ordains. Leibniz argued that God could have created any possible world. Because God is perfect, Leibniz concluded that the actual world must be the best possible world. In addition to his many contributions to logic, Leibniz invented calculus (simultaneously with Newton).1
1. C.Stephen Evans, Pocket Dictionary of Apologetics & Philosophy of Religion (Downers Grove, IL: InterVarsity Press, 2002), pp. 67-68.