Immanuel Kant (1724-1804)
Kant was the ultimate buzzkill of the Enlightenment era. Always talking about categorical imperatives and moral dilemmas. You know, just for fun, he'd ask you to consider a hypothetical scenario, like "If a tree falls in the forest and no one's there to hear it, does it really make a sound?" And then he'd proceed to write 800 pages on it.