German idealism
Neo-Kantianism refers broadly to a revived type of philosophy along the lines of that laid down by Immanuel Kant in the 18th century, or more specifically by Schopenhauer's criticism of the Kantian philosophy in his work "The World as Will and Representation" (1818), as well as by other post-Kantian philosophers such as Jakob Friedrich Fries and Johann Friedrich Herbart. It has some more specific reference in later German philosophy.
Ontological argument
Although a version of the ontological argument appears explicitly in the writings of the ancient Greek philosopher Xenophanes and variations appear in writings by Parmenides, Plato, and the Neoplatonists, the mainstream view is that the ontological argument was first clearly stated and developed by Anselm of Canterbury. Some scholars argued that the Islamic philosopher Avicenna (Ibn Sina) developed a special kind of ontological argument before Anselm, but other scholars have doubted this position. Daniel Dombrowski marked three major stages in the development of the argument: Anselm's initial explicit formulation; the eighteenth-century criticisms of Kant and Hume; and the identification of a second ontological argument in Anselm's "Proslogion" by twentieth-century philosophers.