Since Immanuel Kant (1724–1804) emphasised duty, stressing that valid ethical rules must be applied in all circumstances, he gained a reputation for being dry and humourless. However, that reputation is wrong; he was a great conversationalist, a witty and imaginative lecturer, and an excellent host.

The philosopher Immanuel Kant was probably the profoundest of metaphysicians that the world has yet seen. It was his custom, when deeply engaged upon some abstruse topic, to walk backward and forward, upon a moonlit evening, upon the avenue (bordered on each side with magnificent trees) approaching his house. He was observed, one one occasion, as he slowly, in deep meditation, moved backward and forward along the avenue, to leap over the shadows of the trees as they cast themselves before him in his meditative walk. The delusion was strong upon him that these same shadows were ditches, and that it was incumbent upon him that he should clear them, and that precisely in the way he did. Such are the occasional aberrations of true genius. (source)