The  Laozi , also known as  Tao Te Ching , is a masterpiece of ancient Chinese philosophy as well as the principal religious work of Taoism. It was completed in the early Warring States Period (475–221 BC), but its authorship has been a matter of academic debate. Philosopher Han Fei thought the author was Lao Dan (generally considered to be Laozi), whereas historian Sima Qian raised the possibility that the author could be an imperial historian surnamed Dan, an assumption that has not gained wide recognition.