Hakuin Ekaku (1685-1769) is one of the most influential figures in Zen Buddhism. He revitalized the Rinzai Zen tradition (which emphasizes the use of koans, or unanswerable questions, in meditation practice), and all masters of that school today trace their lineage back through him. He is responsible for the most famous of all koans: What is the sound of one hand clapping? He is also famous for his striking and humorous art, which he also regarded...