The four immortals, namely, Nanhua Zhenren, Chongxu Zhenren, Tongxuan Zhenren, and Dongling Zhenren, are revered by Taoism as the four great immortals.
Nanhua Zhenren was Zhuang Zhou of the pre-Qin Daoist school, whose courtesy name was Zixiu and who was from Song (now northeast of Shangqiu, Henan). He lived at the same time as King Hui of Liang and King Xuan of Qi, and was the magistrate of Qi Yuan in Meng, which belonged to Song during the Spring and Autumn Period and the early Warring States Period, and to Liang during the late Warring States Period. Therefore, Liu Xiang's “Bi Lu” says, “He was also from Meng in Song.” Lu Deming's “Preface to the Classic Commentary” says, “A native of Meng County in the State of Liang.” He then lived in seclusion, was poor, but knowledgeable, and wrote the book “Zhuangzi.” Sima Qian's “Historical Records: Biography of Laozi, Han Feizi, and列传” says his book “has more than 100,000 words, and is largely a collection of fables. The works “Fisherman”, “Thief” and “Pickpocket” were written to discredit the followers of Confucius and to illustrate the teachings of Lao Zi.” In fact, Zhuang Zi was the best successor to Lao Zi's thinking. In history, ‘Lao Zi’ and ‘Zhuang Zi’ were often mentioned together, and together they established a philosophical system with ‘Tao’ at its core. However, Zhuang Zi's thinking was different from Lao Zi's. Lao Zi valued gentleness and advocated avoiding excess and guarding against fullness, seeking to preserve oneself in real relationships. Zhuangzi, on the other hand, believed that real-world relationships were a severe restriction on one's natural nature, and advocated detachment from real-world relationships and a carefree existence. Zhuangzi also regarded “Tao” as the origin of the world, but he did not think that it meant that “Tao” had a material nature. He repeatedly emphasized that Tao is the origin of all things, but it is non-material, and gave the example that “Tao is one with Qi,” but Tao is not Qi, and Qi is derived from Tao. Finally, Zhuangzi focused on the concept of “emptiness”. In “The World of Humans”, he said: “Only the Dao gathers emptiness. Emptiness means a pure mind.” That is, the pursuit of the highest spiritual realm of the “Dao” is to work hard on “emptiness”, to achieve detachment from the world, from material things, from life, to be clear-minded and to see the unique. In this way, one can cultivate the Dao and attain it. This further pushed Lao Zi's thinking to a new level.
In the first year of the Tianbao reign (742–756) of the Tang emperor Xuanzong (742), Zhuangzi was posthumously honored as the South China Sage, and the Zhuangzi was called the “South China Sage Classic.” Emperor Huizong of the Song dynasty posthumously honored him as the “Exquisitely Mysterious and Primordially Pervading True Lord.”
The “Exquisitely Mysterious True Lord” was Lie Zi, a Daoist scholar from the late Spring and Autumn period to the early Warring States period. Lie Zi was named Yukou, also known as Yukou and Yukou, and was from Zheng. He was always poor and looked hungry, but refused the food offered to him by the tyrannical ruler of Zheng. He once asked Guan Yin for teaching and was known for his archery skills. He often exchanged archery experiences and methods with Guan Yin. His book Lie Zi advocated the ideas of quiet and inaction, and independence in the world, which can be summed up as “valuing emptiness” and “valuing correctness”. The Mu Shi Chun Qiu: Bu Er Pian (The Mu Shi Spring and Autumn Annals: The Chapter on Non-Duality) says: “Lie Zi valued emptiness.” This idea advocates getting rid of the shackles of wealth and status, fame and fortune, and letting nature take its course. It regards objective existence as non-existence, and does nothing at all. For example, the Zhuang Zi: Ying Di Wang Pian (Zhuangzi: In Reply to the Emperor) says: “Do nothing to gain fame, do nothing to plan, do nothing to take charge, do nothing to know the master.” The Warring States Policy: Han Ce Er (Warring States Policy: Han Strategy 2) says that Lie Zi valued righteousness in his words to the bandits, which is close to Confucian righteousness.
In the first year of the Tianbao reign (742) of Emperor Xuanzong of the Tang Dynasty, he was conferred the title “True Sage of the Void” and his book was titled “The True Classic of the Void”. In the fourth year (1007) of Emperor Zhenzong's reign (1004–1008) of the Song Dynasty, the two characters “Virtue” were added, and the title became “The True Classic of the Void and Virtue”. Emperor Huizong of the Song Dynasty posthumously conferred the title “True Sage of the Sublime and Wonderful”.
Tongxuan Zhenren, according to legend, was Wen Zi, a representative figure of Huang Lao new Daoism at the end of the Warring States Period, surnamed Xin, named Xuan, also known as Ji Ran, a native of Kuichou, Puyang. Legend has it that he was once a student of Laozi and the teacher of Fan Li. Xin Xuan drew on the strengths of various schools to write the book Wen Zi, continuing to expound on Daoist thought. He expanded on Lao Zi's theory of the Dao, believing that “Tao” is “qi”. For example, “Wenzi · Jiushou” says that “Tao”: “Yao Yao Mingming, Hun Er Wei... The heavy and turbid qi is the earth, the fine and subtle qi is the sky, the essence and spirit are people, and the clear qi is insects.” “Wenzi · Xiade”: “Yin and Yang mold all things, all born from a single qi.” The second is the idea that Lao Tzu's “wu wei” (non-action) is not about sitting still, but rather about eliminating subjective judgments and acting according to objective laws. In the chapter “Nature,” he points out that “the so-called non-action is not about not being able to attract, not being able to push, not being able to respond when pressed, not being able to feel but not move, not being able to flow but being stuck, not being able to grasp but not let go. It means not allowing selfish desires to interfere with justice, not allowing cravings to distort the proper way of doing things, acting according to reason, accomplishing things by using one's abilities, and pushing forward with the momentum of nature.” He also advocated relying on the strength and wisdom of the people to get things done. As the “Lower Chapter” says, “Therefore, what can be lifted with accumulated strength cannot fail; what can be done with the wisdom of the people cannot be unsuccessful.” The “Nature Chapter” says, “With the intelligence of the people, Wu Hu is not strong enough to lift it; with the power of the people, the world is not enough to use it. Therefore, the sage never fails to use the people's resources when he undertakes a task.” His thinking was highly regarded by the society of the time.
In the first year of the Tianbao reign period of the Tang Emperor Xuanzong, he was conferred the title of “Tongxuan Zhenren”. His work was also decreed to be the “Tongxuan Zhenjing”.
Dongling Zhenren was an ancient immortal, also known as Gangsangzi, Gengcangzi, or Gengsangzi. Legend has it that his surname was Gengsang and his given name was Chu, and that he was from the state of Chen. Another legend has it that he was a fictional character in the “Zhuangzi” who had attained the Daosheng Laojun's way and could see and hear with his ears. He retired to Biling Peak and ascended to immortality. Legend has it that he wrote the book “Kang Sang Zi”, and in the first year of the Tianbao reign period of the Tang Emperor Xuanzong, he was bestowed the title “True Sage of the Cave Spirit” in the “True Scripture of the Cave Spirit”.

 四大真人，即南华真人、冲虚真人、通玄真人、洞灵真人，道教尊之为四大真人。
南华真人，为先秦道家学派的庄周，字子休，宋国(今河南商丘东北)人。与梁惠王、齐宣王同时，做过蒙地的漆园吏，蒙地在春秋和战国前期属宋，战国后期属梁。故刘向《别录》称其：“宋之蒙人也。”陆德明《经典释文·序录》称：“梁国蒙县人。”此后他一直隐居，生括贫困，但学识洲博，著《庄子》一书。司马迁《史记·老庄申韩列传》称其书“十万余言，大抵率寓言也。作《渔父》、《盗跖》、《胠箧》以诋孔子之徒，以明《老子》之术。”其实庄子是老子思想的最好继承者，在历史上“老庄”并称，共同建互了以“道”为核心的思想体系。但庄子的思想与老子又有所不同，老子贵柔，主张戒盈防满，在现实关系中求得自身的长保。庄子则认为现实关系是对人的自然本性的严重束缚，主张超脱现实关系而尽情逍遥。庄子同样将“道”视为生天生地的本体，但他又认为并不代表“道”具有物质性，不过是脱离物质而独立存在的精神。他多次强调道是产生万物的本体，但它是非物质的，并举例说“道通一气”，但道并不是气，气是自道派生的。最后庄子将道集中“虚”上，他在《人间世》中说：“唯道集虚。虚者，心斋也。”即追求“道”的最高精神境界，在务“虚”上下功夫，做到外天下、外物、外生、朝彻、见独，从而修道、得道。进而把老子的思想推向一个新的层次。
唐玄宗天宝(742—756年)元年(742年)追封庄子为南华真人，称《庄子》为《南华真经》宋徽宗追封为其为“微妙元通真君”。
冲虚真人，为春秋末至战国前期道家学者列子。列子名御寇，亦名圄寇、圉寇，郑国人。一向家贫，面带饥色，但拒绝郑国暴虐执政者馈赠的粮食。他曾向关尹请教学问，以善射著称，常常与关尹切磋射箭经验与方法。其著《列子》一书，主张清静无为、独立处世之思想，概括起来为“贵虚”和“贵正”。《目氏春秋·不二篇》曰：“列子贵虚。”这种思想主张摆脱人世问贵贱、名利的羁绊，任其自然，把客观存在看作不存在，一切无所作为。如《庄子·应帝王篇》：“无为名尸，无为谋府，无为事任，无为知主。”《战国策·韩策二》称列子圉寇之言“贵正”，则近于儒家正名。
唐玄宗天宝元年封为“冲虚真人”，号其书为《冲虚真经》。宋真宗景德(1004—1008年)四年(1007年)加“至德”二字，号为《冲虚至德真经》。宋徽宗追封为“致虚观妙真君”。
通玄真人，据传为战国末黄老新道家的代表人物文子，姓辛名銒，一名计然，葵丘濮上人。相传曾受业于老子，范蠡之师。辛銒博采众家之长，著《文子》一书，继续阐扬道家思想。他对老子的道论有所发挥，认为“道”即“气”。如《文子·九守》说“道”：“窈窈冥冥，浑而为一……重浊之气为地，精微之气为天，精气为人，清气为虫。”《文子·下德》：“阴阳陶冶万物，皆乘一气而生。”其次认为老子的无为“并非坐着不动，而是排除主观臆断，按客观规律办事，在《自然》篇中，他指出“所谓无为者，非谓其引之不来，推之不往，迫而不应，感而不动，坚滞而不流，卷握而不散也，谓其私志不入公道，嗜欲不枉正术，循理而举事，因资而立功，推自然之势也。”并主张依靠众人的力量和智慧来办事，如《下篇》曰：“故积力之所举，即无不胜也；众智之所为，即无不成也。” 《自然篇》曰：“用众人之智力，乌获不足持也；乘众人之势，天下不足用也。故圣人举事，未尝不因其资而用之也。”他这种思想得到了当时社会的推崇。
唐玄宗天宝元年封其为通玄真人。诏封其著为《通玄真经》。
洞灵真人，为古代仙人，又称亢桑子、亢仓子、庚桑子。传说他姓庚桑，名楚，陈国人。又传说为《庄子》中的寓言人物，得太上老君之道，能以耳视目听。隐居毗陵峰，登仙而去。相传《亢桑子》一书自其所著，唐玄宗天宝元年诏封为《洞灵真经》封其为“洞灵真人”。