The philosopher German referred to in the crossword solution is Immanuel Kant, an 18th century philosopher from Königsberg, Prussia (now Kaliningrad, Russia). He is widely regarded as one of the most influential thinkers of modern Europe and his work has been a major influence in the development of many philosophical movements. Kant's most famous works include Critique of Pure Reason, Groundwork of the Metaphysics of Morals, and Prolegomena to Any Future Metaphysics.