Once Zhuangzi dreamt he was a butterfly, a butterfly flitting and fluttering around, happy with himself and doing as he pleased. He didn't know he was Zhuangzi. Suddenly he woke up and there he was, solid and unmistakable Zhuangzi. But he didn't know if he was Zhuangzi who had dreamt he was a butterfly, or a butterfly dreaming he was Zhuangzi.
Zhuangzi was a Chinese Taoist philosopher of the Warring States period with a deep influence on Chinese Buddhism. He was famous for telling parables and inventing koans. A few centuries later, Zhuangzi's style got mixed up with Mahayana Buddhist theology to create the school of Chán, known to the West by its Japanese name: Zen.
However, in the West, he is best known as the man who couldn't figure whether he was a butterfly and is hence half the Trope Namer for Schrodinger's Butterfly and proof that All Just a Dream is Older Than Feudalism.