Priests of the Vedic religion are officiants of the yajna service. As persons trained for the ritual and proficient in its practice, they were called ṛtvij ("regularly-sacrificing"). As members of a social class, they were generically known as vipra ("sage") or kavi ("seer"). Specialization of roles attended the elaboration and development of the ritual corpus over time. Eventually a full complement of sixteen ṛtvijas became the custom for major ceremonies. The sixteen consisted of four chief priests and their assistants.
Chief priests 
The older references uniformly indicate the hotṛ as the presiding priest, with perhaps only the adhvaryu as his assistant in the earliest times. The phrase "seven hotars" is found more than once in the Rgveda. RV 2.1.2 enumerates them as the hotṛ, potṛ, neṣṭṛ, agnīdh, prashāstṛ (meaning the maitrāvaruna), adhvaryu and brahman (meaning the brāhmanācchamsin).
- The hotṛ was the reciter of invocations and litanies. These could consist of single verses (ṛca), strophes (triples called tṛca or pairs called pragātha), or entire hymns (sukta), drawn from the ṛgveda. As each phase of the ritual required an invocation, the hotṛ had a leading or presiding role.
- The adhvaryu was in charge of the physical details of the sacrifice (in particular the adhvara, a term for the Somayajna). According to Monier-Williams, the adhvaryu "had to measure the ground, to build the altar, to prepare the sacrificial vessels, to fetch wood and water, to light the fire, to bring the animal and immolate it," among other duties. Each action was accompanied by supplicative or benedictive formulas (yajus), drawn from the yajurveda. Over time, the role of the adhvaryu grew in importance, and many verses of the ṛgveda were incorporated, either intact or adapted, into the texts of the yajurveda.
- The udgātṛ was a chanter of hymns set to melodies (sāman) drawn from the sāmaveda. This was a specialized role in the major soma sacrifices: a characteristic function of the udgātṛ was to sing hymns in praise of the invigorating properties of soma pavamāna, the freshly pressed juice of the soma plant.
- The brahman was superintendent of the entire performance, and responsible for correcting mistakes by means of supplementary invocations.
The rgvedic Brahmanas, Aitareya and Kausitaki, specify seven hotrakas to recite shastras (litanies): hotṛ, brāhmanācchamsin, maitrāvaruna, potṛ, neṣṭṛ, agnīdh and acchāvāka. They also carry a legend to explain the origin of the offices of the subrahmanya and the grāvastut.
A similar attempt at symmetry, as well as an attempt to inflate the importance of the Atharvaveda, was a claim (in the Gopatha Brahmana) that this veda was the province of the brahman: allegedly, just as specific vedas were associated with the other three chief priests, the Atharvaveda was the fourth and presumably superior veda for the fourth and senior most of the chief priests. This theoretical fancy had no basis in fact or likelihood, as the Atharvaveda made no contribution to the liturgy of the solemn high rituals. In practice, the brahman function was usually performed by a bahvṛca ("one who has many verses", i.e. a Rgvedin), suggesting a historical split of the duties of the hotṛ in the development of the brahman as a distinct role.
Note that the Vedic accent is distinctive in this case, the name of the priest is brahmán, as opposed to (and morphologically derived from) the term bráhman "sacred utterance" (and hence "Universal Soul", etc.).
The requirements of the fully developed ritual were rigorous enough that only professional priests could perform them adequately. Thus, whereas in the earliest times, the true sacrificer, or intended beneficiary of the rite, might have been a direct participant, in Vedic times he was only a sponsor, the yajamāna, with the hotṛ or brahman taking his stead in the ritual. In this seconding lay the origins of the growing importance of the purohita (literally, "one who is placed in front"), a term originally for a domestic chaplain, especially of a prince. It was not unusual for a purohita to be the hotṛ or brahman at a sacrifice for his master, besides conducting other more domestic (gṛhya) rituals for him also. In latter days, with the disappearance of vedic ritual practice, purohita has become a generic term for "priest".
In the systematic expositions of the shrauta sutras,  which date to the fifth or sixth century BCE, the assistants are classified into four groups associated with each of the four chief priests, although the classifications are artificial and in some cases incorrect:
- With the hotṛ:
- the maitrāvaruna
- the acchāvāka
- the grāvastut (praising the Soma stones)
- With the udgātṛ:
- the prastotṛ (who chants the Prastâva)
- the pratihartṛ ("averter")
- the subrahmanya
- With the adhvaryu:
- the pratiprasthātṛ
- the neṣṭṛ
- the unnetṛ (who pours the Soma juice into the receptacles )
- With the brahman:
- the brāhmanācchamsin
- the agnīdh (priest who kindles the sacred fire)
- the potṛ ("purifier")
This last classification is incorrect, as the formal assistants of the brahman were actually assistants of the hotṛ and the adhvaryu.[clarification needed]
Philological comparisons 
Comparison with the sacred texts of Zoroastrianism, a distinct religion with the same origins, shows the antiquity of terms for priests such as atharvan (cognate to Avestan athravan) and hotar (Av. zaotar) "invoker, sacrificer". While hotar/zaotar is well understood, the original meaning of atharvan/athravan is unknown. The word atharvan appears in the Rig Veda (e.g., in RV 6.16.13 where Agni is said to have been churned by Atharvan from the mind of every poet). In the Younger Avesta appears in a context that suggests "missionary," perhaps by metathesis from Indo-Iranian *arthavan "possessing purpose." In the Upanishads, the term appears for example in atharvāngiras, a compound of atharvan and angiras, either two eponymous rishis or their family names.
In present-day Indian Zoroastrian (Parsi) tradition the word athornan is used to distinguish the priesthood from the laity (the behdin). These subdivisions (in the historical Indian context, castes), and the terms used to describe them, are relatively recent developments specific to Indian Zoroastrians and although the words themselves are old, the meaning that they came to have for the Parsis are influenced by their centuries-long coexistence with Hinduism. It appears then that the Indian Zoroastrian priests re-adopted the older athravan (in preference to the traditional, and very well attested derivative asron) for its similarity to Hinduism's arthavan, which the Parsi priests then additionally assumed was derived from Avestan atar "fire". This folk-etymology, which may "have been prompted by what is probably a mistaken assumption of the importance of fire in the ancient Indo-Iranian religion" (Boyce, 1982:16).
There is no evidence to sustain the supposition that the division of priestly functions among the Hotar, the Udgatar and the Adhvaryu is comparable to the Celtic priesthood as reported by Strabo, with the Druids as high priests, the Bards doing the chanting and the Vates performing the actual sacrifice.
- Shānkhāyana SS 13.4.1, Āsvalāyana SS 4.1.4-6.
See also 
- e-learning of Basic Vedic Mantras & rituals from Home for Brahmins Online Vedic Courses through Video Conferencing by Vedic Priests
- The Turning-Point in a Living Tradition