Katyayana was born in the kingdom of Avanti in southern India. His father was the royal preceptor for the king, so his family was very rich. When he was young, he started learning all sorts of religious philosophy from his uncle, Asita. Asita knew that Prince Siddhartha would attain buddhahood and be the savior of the world. He told Katyayana that he had to follow the Buddha and learn about the Truth of the universe from him. From his uncle, Katyayana was able to attain supernatural powers and a great power of meditation, so when he talked to the Buddha for the first time, he attained the arhathood. He was renowned for being the best at giving lectures and commentaries, because he was able to comment on and spread the Buddha's teachings.

 Katyayana was also very good with language. Before he became the Buddha's disciple, an old stone with an inscription in an archaic language was discovered near Varanasi. No one knew what was written on the stone, so the king announced that whoever could decipher the inscription would be rewarded. When Katyayana heard about this, he went to the king and translated the inscription, which was as follows:

Who is the sage among all sages?
Who is a stupid person?
Who is a wise person?
Who is constantly reincarnated?
Who is constantly at ease?
How can one be free from the defilement of this world?
How can one attain nirvana?

Katyayana's translation amazed the whole kingdom, but he still did not understand the answers to the questions. At that time, the Buddha came to Avanti. Katyayana recalled what his uncle had told him earlier, so he went with the king to visit the Buddha, who instantly explained the inscription with another verse:

The sage among all the sages is a buddha.
A stupid person is one tainted by ignorance.
A wise person is one who knows how to eradicate worry.
Anyone who clings to his attachments to egoism and doctrine is constantly reincarnated.
Anyone who realizes that everything in the world is the result of conditions and thus is impermanent in its substance can be at ease at all times.
Doing spiritual cultivation to the extent of eliminating greed, anger and delusion can free one from the defilement of this world.
By diligently cultivating the precepts, meditation and wisdom, one can attain nirvana.

When Katyayana heard the Buddha's reply, he was filled with tranquility and joy because the reply had helped him to understand the truth of the world better, and he immediately attained enlightenment. He asked the Buddha whether he could become his disciple. The Buddha kindly accepted him and he became the Buddha's great assistant.

One day, he was walking on the street and ran into a Brahman."I'm very glad to see you, because I have a question for you," the Brahman said."I hope you can answer it objectively."

"What is it?"
"I see members of the Kshatriya caste fighting among themselves and the Brahmans fighting among themselves, too. Why is that?"
"Because of greed."
"Then, why do monks argue among themselves?"
"Because of their attachments to their personal views and doctrines."
The Brahman closed his eyes, pondering this answer, and he seemed very satisfied. Then he spoke again."Your answer was very fair. But I want to know who in this world is free from both?"
"My teacher, the Buddha, who is now teaching in Sravasti. He is enlightened and has neither greed nor ego. He is the teacher for us humans and for the celestial beings."

 The Brahman was happy with this answer and decided to become the Buddha's disciple.

Another time, a ferocious old Brahman came to see Katyayana because he had heard that he was very good at commentary. "I heard that you were originally a Brahman, but now you don't worship the Brahman gods anymore. You don't prostrate yourself in front of a Brahman priest like me anymore. I don't like that. That's why I am asking you whether this is true."

Katyayana replied with confidence."You are right that I, originally a Brahman, have become a Buddhist monk and I don't worship the Brahman gods any more. You cannot judge me by my youthful appearance, because I have fully awakened to the Truth of the universe. If an eighty-or ninety-year-old Brahman is still full of greed, anger and delusion, as well as other lusts, why should he be respected at all."