​Gautama Buddha, also known simply the Buddha, was a sage 

on whose teachings Buddhism was founded. He is believed to

have lived and taught mostly in the eastern part of the 

Indian Subcontinent sometime between the sixth and fourth

centuries BCE.

For what reason why the Buddha arose in the world? 

The Buddha clearly clarified for bhikkhus;

 

"Bhikkhus, if these three things were not found in the
world, the Tathagata, the Arahant, the Perfectly

Enlightened One would not arise in the world, and

the Dhamma and discipline proclaimed by him would not shine

in the world. What three?

 

Birth, old age, and death. If these three things were not

found in the world, the Tathagata, the Arahant, the

Perfectly Enlightened One would not arise in the world, and

the Dhamma and discipline proclaimed by him would not

shine in the world. But because these three things are

found in the world, the Tathagata, the Arahant,

the Perfectly Enlightened One arises in the world, and

the Dhamma and discipline proclaimed by him shines

in the world."[1]

 

What does the word "Buddha" exactly mean?

The Gautama Buddha clarified for the brahmin Dona;

"I have destroyed those taints by which I might have been

reborn as a deva or as a gandhabba that travels through

the sky; by which I might have reached the state of

a yakkha,or arrived back at the human stated:I have

dispelled and cut down these taints.

"As a lovely white lotus is not soiled by the water,I am not soiled by the world: therefore, O brahmin,I am a Buddha."[2]

 

The word Buddha also means "awakened one"or"the enlightened one".The Gautama Buddha taught a Middle Way between sensual indulgence and the severe asceticism found in the śramaṇa movement common in his region. He later taught throughout regions of eastern India such as Magadha and Kosala.

 

Gautama is the primary figure in Buddhism and accounts of his life, discourses, and monastic rules are believed by Buddhists to have been summarized after his death and memorized by his followers. Various collections of teachings attributed to him were passed down by oral tradition and first committed to writing about 400 years later.

 

Buddhavacana is the discourses from the Buddha's mouth without adding any disciple'words. For example,the Buddha said to bhikkhus,

 

 "Bhikkhus do not authorise what has not been authorised already, and do not abolish what has been authorised, but proceed according to what has been authorised by the rules of training. As long as you hold to these things and are seen to do so, you may be expected to prosper and not decline."[3]

 

Moreover, the Blessed One also clarified for Ananda bhikkhu,

 

 "Ananda, it may be that you will think: "The Teacher's instruction has ceased, now we have no teacher!" It should not be seen like this, Ananda, for what I have taught and explained to you as Dhamma and discipline will, at my passing, be your teacher.[4]

 

Ref: 

[1] Bodhi, B. (2012). The Numerical Discourses of the Buddha: A Complete Translation of the Anguttara Nikaya        (Teachings of the Buddha) Boston : Wisdom Publications. 1434-1435

[2] Bodhi, B. (2012). The Numerical Discourses of the Buddha: A Complete Translation of the Anguttara Nikaya  (Teachings of the Buddha) Boston : Wisdom Publications. 425-426

[3] Walshe, MO 1995, The Long Discourses Of The Buddha : A Translation Of The Dīgha Nikāya, n.p.: Boston : Wisdom    Publications, 1995.232-233

[4] Walshe, MO 1995, The Long Discourses Of The Buddha : A Translation Of The Dīgha Nikāya, n.p.: Boston : Wisdom  Publications, 1995.269-270