The Buddha taught in the Uposatha Sutta,
"And furthermore, just as the ocean is the abode of such mighty beings as whales, whale-eaters, and whale-eater-eaters; asuras, nagas, and gandhabbas, and there are in the ocean beings one hundred leagues long, two hundred... three hundred... four hundred... five hundred leagues long; in the same way, this Doctrine and Discipline is the abode of such mighty beings as stream-winners and those practicing to realize the fruit of stream-entry; once-returners and those practicing to realize the fruit of once-returning; non-returners and those practicing to realize the fruit of non-returning; Arahants and those practicing for Arahantship. The fact that this Doctrine and Discipline is the abode of such mighty beings as stream-winners and those practicing to realize the fruit of stream-entry; once-returners and those practicing to realize the fruit of once-returning; non-returners and those practicing to realize the fruit of non-returning; Arahants and those practicing for Arahantship: This is the eighth amazing and astounding fact about this Doctrine and Discipline that, as they see it again and again, has the monks greatly pleased with the Doctrine and Discipline."
These eight individuals are the true representatives of the Buddha Dhamma, namely,
1) & 2) stream-winners
3) & 4) once-returners
5) & 6) non-returners
7) & 8) arahants
However, it must be clarified here that those who are not practicing the right path to realize nibbāna are not included here, and merely "aspiring" to become one of the four Noble Ones is NOT one of the eight individuals.
One must be practicing the Eightfold Noble Path to a certain extent in order to be recognized as one of the eight individuals.
The "Noble Ones" means the ones who have attained one of the Four Noble Fruits, and they are:
1) The stream-winner (sotapanna): is one who has become free from the first three of the ten fetters which bind beings to the sensuous sphere, namely, personality belief, sceptical doubt, and attachment to mere rules and rituals. At this stage, one has realized nibbāna for the first time, and there are 7 more rebirths utmost.
2) The once-returner (sakadagami): has weakened the fourth and fifth of the ten fetters, sensuous craving and ill-will. There are two more rebirths utmost.
3) The non-returner (anagami): becomes fully free from the above-mentioned five lower fetters and is no longer reborn in the sensuous sphere. There are one more rebirth utmost.
4) Arahantship: through the path of arahant one further becomes free of the last five fetters: craving for fine-material existence (in celestial worlds), craving for immaterial (purely mental) existence, conceit, restlessness, and ignorance. There is no more rebirth.
These are the four Noble Persons in Buddhism, and they are the ones who have personally realized nibbāna in this very life.
"These are the eight amazing and astounding facts about this Doctrine and Discipline that, as they see them again and again, have the monks greatly pleased with the Doctrine and Discipline."
