Laozi is traditionally known as the founder of Taoism, but a lot of modern historians believe that Laozi never existed at all as a historical figure. He is best known as the author of the Tao Te Ching, but the Tao Te Ching is regarded as a collection of writings by many different wise people. The first reliable record of a biography of Laozi is found in the Shiji, or Records of the Historian, written by Sima Qian around 100 B.C.E. He appears several times in the Shiji, sometimes as a contemporary of Confucius and sometimes as the Grand Historian and astrologer Lao Dan.
Chuang Tzu, more commonly known as Zhuangzi, was an influential Daoist philosopher around 3rd century BCE. He is credited with writing a work known by his name, the Zhuangzi, which argues that life is limited and knowledge to be gained is unlimited. In a well-known part of the book, usually called "Zhuangzi dreamed he was a butterfly", contains a famous phrase, "But he didn't know if he was Zhuangzi who had dreamt he was a butterfly, or a butterfly dreaming he was Zhuangzi."