A Luohan, the Chinese word for arhat, in Buddhism, is a Buddhist disciple who have achieved the Buddhist enlightened state of 'Nirvana', which is the state of perfect blessedness achieved by the extinction of individual existence and all human desires and passions, or "enlightened beings who act as worldly conduits to the state of infinitely expanded consciousness granted by their enlightenment".
Luohans (in older texts Lohan) are usually depicted in grouping of 16, 18, or 500, and are based on real Indian holy men. Numbers vary in Buddhist iconography, but a group of eighteen was eventually established as the standard Chinese grouping which became popular in later Chinese art. They are frequently seen in paintings, as statues in temples and in general appear in a wide variety of media.
In Michael Butler, Curtis and Little, Shunzhi Porcelain: Treasures from an Unknown Reign, 1644-1661, Alexandria, VA, 2002, pp. 218-219, no. 71) Dr. Julia B. Curtis notes that the depiction of the Eighteen Lohans became a popular theme with painters of the late sixteenth century such as Wu Bin and Ding Yungpeng, both of whom were Buddhists from gentry families who earned their livelihoods as painters. During the late sixteenth and seventeenth centuries, Chinese Buddhism underwent an important period of doctrinal change, particularly the syncretism of Chan with Pure land sectarianism, and, in society at large, of Buddhism, Daoism, and Confucianism. The openness of Buddhism to "the unity of the three teachings" (sanjiao heyi) dignified the religion in the eyes of the scholar-gentry, which may account for the popularity of Buddhist motifs in the decorative arts and in professional paintings of the period.