user11541: Every book says that Siddhartha Gautama achieved Nirvana and then became Gautama Buddha. But now that I have realized that all phenomenon are nonself , it becomes imperative for me to ask : did Siddhartha Gautama achieve Nirvana?
NOTE: It is not a duplicate of question "who or what achieves enlightenment?" because I am asking the question in relation to only and only Siddhartha Gautama. In the question "who or what achieves enlightenment?" Siddhartha Gautama is not mentioned and nobody answers for it.

user-1: The Buddha achieved nirvana, yes. I think all Buddhists would agree.
Supposing that you definitely mean "Guatama" to refer not to a person but a sequence of conditioned phenomema, I suppose you can say that, though it might imply something like buddha nature, that his enlightened nature existed before it was attained. Just a note to add:

I have realized that all phenomenon are nonself

I believe that the Buddha does say, in some suttas, "I have", so this makes sense to assert, whether or not it's true! If your question is best answered via saying what that "I" means, when Buddhas say it, I personally feel it refers to Buddha nature, and not the bodhisattva that has fulfilled its vows and been used up.
Thanks!

user254: The enlightened Buddha told people to address him as "the Tathagata":

One, standing up to greet me, received my robe & bowl. Another spread out a seat. Another set out water for washing my feet. However, they addressed me by name and as 'friend.'
"So I said to them, 'Don't address the Tathagata  by name and as "friend." The Tathagata, friends, is a worthy one, rightly self-awakened. Lend ear, friends: the Deathless has been attained. I will instruct you. I will teach you the Dhamma.

See also this topic: Why does the Buddha call himself the Tathāgata?

Some Buddhist talk about "being" using the parable of the chariot:

Just as, with an assemblage of parts,
The word 'chariot' is used,
So, when the aggregates are present,
There's the convention 'a being.'

In context though that seems to be a description of how (or whether) she sees herself. A "name" may be part of that (i.e. your name may be part of how you see yourself), but a name is mostly used (and needed) by other people: to address you, to refer to you in stories, to attribute words to you and so on.

11541: <p>Every book says that Siddhartha Gautama achieved Nirvana and then became Gautama Buddha. But now that I have realized that all phenomenon are nonself , it becomes imperative for me to ask : did Siddhartha Gautama achieve Nirvana?</p>

<p>NOTE: It is not a duplicate of question <a href="https://buddhism.stackexchange.com/questions/7986/if-there-is-no-self-what-or-who-is-it-that-gets-enlightened">"who or what achieves enlightenment?"</a> because I am asking the question in relation to only and only Siddhartha Gautama. In the question "who or what achieves enlightenment?" Siddhartha Gautama is not mentioned and nobody answers for it.</p>
 -1: <p>The Buddha achieved nirvana, yes. I think all Buddhists would agree.</p>

<p>Supposing that you definitely mean "Guatama" to refer not to a person but a sequence of conditioned phenomema, I suppose you <em>can</em> say that, though it might imply something like buddha nature, that his enlightened nature existed before it was attained. Just a note to add:</p>

<blockquote>
  <p>I have realized that all phenomenon are nonself</p>
</blockquote>

<p>I believe that the Buddha <em>does</em> say, in some suttas, "I have", so this makes sense to assert, whether or not it's true! If your question is best answered via saying what that "I" means, when Buddhas say it, I personally feel it refers to Buddha nature, and not the bodhisattva that has fulfilled its vows and been used up.</p>

<p>Thanks!</p>
 254: <p>The enlightened Buddha <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.026.than.html" rel="nofollow noreferrer">told people to address him</a> as &quot;the Tathagata&quot;:</p>
<blockquote>
<p>One, standing up to greet me, received my robe &amp; bowl. Another spread out a seat. Another set out water for washing my feet. However, they addressed me by name and as 'friend.'</p>
<p>&quot;So I said to them, 'Don't address the Tathagata  by name and as &quot;friend.&quot; The Tathagata, friends, is a worthy one, rightly self-awakened. Lend ear, friends: the Deathless has been attained. I will instruct you. I will teach you the Dhamma.</p>
</blockquote>
<p>See also this topic: <a href="https://buddhism.stackexchange.com/q/1629/254">Why does the Buddha call himself the Tathāgata?</a></p>
<hr />
<p>Some Buddhist talk about &quot;being&quot; using the <a href="https://en.wikipedia.org/wiki/Vajira_(Buddhist_nun)" rel="nofollow noreferrer">parable of the chariot</a>:</p>
<blockquote>
<p>Just as, with an assemblage of parts,<br />
The word 'chariot' is used,<br />
So, when the aggregates are present,<br />
There's the convention 'a being.'</p>
</blockquote>
<p>In context though that seems to be a description of how (or whether) she sees herself. A &quot;name&quot; may be part of that (i.e. your name may be part of how you see yourself), but a name is mostly used (and needed) by other people: to address you, to refer to you in stories, to attribute words to you and so on.</p>
