A semi-legendary figure, Laozi was usually portrayed as a 6th-century BC contemporary of Confucius, but most modern historians consider him to have lived during the Warring States period of the 5th or 4th century BC. A central figure in Chinese culture, Laozi is claimed by both the emperors of the Tang dynasty and modern people of the Li surname as a founder of their lineage. Laozi's work has been embraced by both various anti-authoritarian movements and Chinese Legalism.
In traditional accounts, Laozi's personal name is usually given as Li Er (李耳, Old *Rəʔ Nəʔ, Mod. Lǐ Ěr) and his courtesy name as Boyang (trad. 伯陽, simp. 伯阳, Old *Pˤrak-lang, Mod. Bóyáng). A prominent posthumous name was Li Dan (李聃, Lǐ Dān).
Laozi itself is a honorific title: 老 (Old *rˤuʔ, "old, venerable") and 子 (Old *tsə′, "master"). It is usually pronounced // in English. It has been romanized numerous ways, sometimes leading to confusion. The most common present form is Laozi or Lǎozǐ, based on the Hanyu Pinyin system adopted by Mainland China in 1958 and by Taiwan in 2009. During the 20th century, Lao-tzu was more common, based on the formerly prevalent Wade–Giles system. In the 19th century, the title was usually romanized as Lao-tse. Other forms include the variants Lao-tze and Lao-tsu.
As a religious figure, he is worshipped under the name "Supreme Old Lord" (太上老君, Tàishàng Lǎojūn) and as one of the "Three Pure Ones." During the Tang Dynasty, he was granted the title "Supremely Mysterious and Primordial Emperor" (太上玄元皇帝, Tàishàng Xuānyuán Huángdì).
In the mid-twentieth century, a consensus emerged among scholars that the historicity of the person known as Laozi is doubtful and that the Tao Te Ching was "a compilation of Taoist sayings by many hands." Philosopher Alan Watts urged more caution, holding that this view was part of an academic fashion for skepticism about historical spiritual and religious figures and stating that not enough would be known for years – or possibly ever – to make a firm judgment.