Shudra is the fourth varna, whose mythological origins are described in the Purusha Sukta of the Rig veda, one of the sacred texts of Hinduism, and later explained in the Manusmṛti. This latter text defines society as comprising four groups, sometimes also called chaturvarna, of which the other three are Brahmins (priests), Kshatriya (those with governing functions) and Vaishya (agriculturalists, cattle rearers and traders). According to this ancient text, the Shudra perform functions of serving the other three varna.
The Rig veda was compiled over a considerable period and it is generally agreed that the Purusha Sukta, which is the only hymn in the Rig Veda which mentions the varnas, was added during the Mantra period, the period immediately preceding the Brahmana period, or the beginning of the post-vedic age. Since the varnas are first mentioned in the Purusha Sukta, it is evident that they did not exist before the Mantra period.
The relationship between occupation, varna, and social ordering in the Rig Vedic period is complex. In the varna ordering of society, notions of purity and pollution were central. The phenomenon of the upper classes living on the labour of tribesmen was just emerging, and was not ritualized or ideologically ratified until the Purusha Sukta. R. S. Sharma states that "the Rig Vedic society was neither organized on the basis of social division of labour nor on that of differences in wealth... [it] was primarily organised on the basis of kin, tribe and lineage."
The varna system became rigid in the later Vedic period. In modern Indian society, the government is taking steps to end these distinctions.
Ambedkar, a polymath and a Dalit activist, believed that there were initially only three varnas: the Brahmin, Kshatriya and Vaishya, and that the Shudras were the Kshatriyas who were denied the Upanayana, an initiation ritual, by the Brahmins. This claim has been contested by historians such as Sharma.
The tenets of Vedic Hinduism in north India held less sway in the south, where the societal divisions were simply Brahmin and Shudra. However, some non-Brahmins adopted the classification of Sat Shudra (clean Shudra) in an attempt to distinguish themselves from other non-Brahmin communities.