What is "upali"

Upali ( Sanskrit उपालि upāli) was a monk, one of the ten chief disciples of the Buddha. Before joining the order, he was part of the Royal barber caste and worked as a barber. When he cut the Buddha's hair, the Buddha told that he was breathing too fast. So, he learned how to control his mind by controlling his breathing. Later, he asked the Buddha if a person of "low birth" such as he could join the order. The Buddha ordained him before the princes and asked the princes to pay homage to Upali, who by then had become an Arhant and was an elder compared to the seven princes. He became the chief disciple in knowing the rules of the order and the foremost disciple in keeping precepts, later developing the Vinaya School.