user5866: Before Siddhartha Gautama became The Omniscient Buddha, did he believe in, support and uphold the religious beliefs that the commoners and/or learned persons practiced at the time that he lived?
Or alternatively, did he question the established religious beliefs of his time, and in his culture?
In other words, did Siddhartha Gautama arrive at his Enlightenment by BELIEVING in prevailing religious mythology and principles, or did he arrive at his Enlightenment by QUESTIONING, EXAMINING and REJECTING them?  

user6923: As of my understanding,

In other words, did Siddhartha Gautama arrive at his Enlightenment by
  BELIEVING in prevailing religious mythology and principles

No. He tried many teachers. But he couldn't find what he is looking for. So ultimately he himself found the what he looked for.

did he arrive at his Enlightenment by QUESTIONING, EXAMINING and
  REJECTING them?

No for this too. He found his enlightenment by himself. Not by questioning, examining someone else. He didn't directly go to Jungle and start meditation nor he questioned from the very first moment from other teachers. He tried patiently. And once he understood that this is not he was looking for, he left. He did this several times. Finally he decided to search it by himself and arrived at his enlightenment. 

user254: The Ariyapariyesana Sutta: The Noble Search is a partial description of his quest for enlightenment.
It contains passages like the following,

"Having thus gone forth in search of what might be skillful, seeking
  the unexcelled state of sublime peace, I went to Alara Kalama and, on
  arrival, said to him: 'Friend Kalama, I want to practice in this
  doctrine & discipline.'
"When this was said, he replied to me, 'You may stay here, my friend.
  This doctrine is such that a wise person can soon enter & dwell in his
  own teacher's knowledge, having realized it for himself through direct
  knowledge.'
"It was not long before I quickly learned the doctrine. As far as mere
  lip-reciting & repetition, I could speak the words of knowledge, the
  words of the elders, and I could affirm that I knew & saw — I, along
  with others.
"I thought: 'It isn't through mere conviction alone that Alara Kalama
  declares, "I have entered & dwell in this Dhamma, having realized it
  for myself through direct knowledge." Certainly he dwells knowing &
  seeing this Dhamma.' So I went to him and said, 'To what extent do you
  declare that you have entered & dwell in this Dhamma?' When this was
  said, he declared the dimension of nothingness.
"I thought: 'Not only does Alara Kalama have conviction, persistence,
  mindfulness, concentration, & discernment. I, too, have conviction,
  persistence, mindfulness, concentration, & discernment. What if I were
  to endeavor to realize for myself the Dhamma that Alara Kalama
  declares he has entered & dwells in, having realized it for himself
  through direct knowledge.' So it was not long before I quickly entered
  & dwelled in that Dhamma, having realized it for myself through direct
  knowledge. I went to him and said, 'Friend Kalama, is this the extent
  to which you have entered & dwell in this Dhamma, having realized it
  for yourself through direct knowledge?'
"'Yes, my friend...'
"'This, friend, is the extent to which I, too, have entered & dwell in
  this Dhamma, having realized it for myself through direct knowledge.'
"'It is a gain for us, my friend, a great gain for us, that we have
  such a companion in the holy life. So the Dhamma I declare I have
  entered & dwell in, having realized it for myself through direct
  knowledge, is the Dhamma you declare you have entered & dwell in,
  having realized it for yourself through direct knowledge. And the
  Dhamma you declare you have entered & dwell in, having realized it for
  yourself through direct knowledge, is the Dhamma I declare I have
  entered & dwell in, having realized it for myself through direct
  knowledge. The Dhamma I know is the Dhamma you know; the Dhamma you
  know is the Dhamma I know. As I am, so are you; as you are, so am I.
  Come friend, let us now lead this community together.'
"In this way did Alara Kalama, my teacher, place me, his pupil, on the
  same level with himself and pay me great honor. But the thought
  occurred to me, 'This Dhamma leads not to disenchantment, to
  dispassion, to cessation, to stilling, to direct knowledge, to
  Awakening, nor to Unbinding, but only to reappearance in the dimension
  of nothingness.' So, dissatisfied with that Dhamma, I left.
"In search of what might be skillful, seeking the unexcelled state of
  sublime peace, I went to Uddaka Ramaputta and, on arrival, etc.

In other words he studied with various teachers, and successfully learned what they were teaching, but wasn't satisfied (and therefore went to another teacher, etc.).


In other words, did Siddhartha Gautama arrive at his Enlightenment by BELIEVING in prevailing religious mythology and principles, or did he arrive at his Enlightenment by QUESTIONING, EXAMINING and REJECTING them?

I think he started by learning teachers' doctrines and practices, but (having understood them) finding them unsatisfactory.

user111: There's no belief for a Buddha. A Buddha is omniscient. He knows what is right and what is wrong by direct knowledge.
Yes, the Buddha did uphold certain religious practices of the time which are congenial to the path.
ex: The five precepts, 13 Dutangas, attainment of the Janas
He also rejected many false views which the contemporary religions were based on. They are grouped into 62 in Brahmajāla sutta.

5866: <p>Before Siddhartha Gautama became The Omniscient Buddha, did he believe in, support and uphold the religious beliefs that the commoners and/or learned persons practiced at the time that he lived?</p>

<p>Or alternatively, did he question the established religious beliefs of his time, and in his culture?</p>

<p>In other words, did Siddhartha Gautama arrive at his Enlightenment by BELIEVING in prevailing religious mythology and principles, or did he arrive at his Enlightenment by QUESTIONING, EXAMINING and REJECTING them?  </p>
 6923: <p>As of my understanding,</p>

<blockquote>
  <p>In other words, did Siddhartha Gautama arrive at his Enlightenment by
  BELIEVING in prevailing religious mythology and principles</p>
</blockquote>

<p>No. He tried many teachers. But he couldn't find what he is looking for. So ultimately he himself found the what he looked for.</p>

<blockquote>
  <p>did he arrive at his Enlightenment by QUESTIONING, EXAMINING and
  REJECTING them?</p>
</blockquote>

<p>No for this too. He found his enlightenment by himself. Not by questioning, examining someone else. He didn't directly go to Jungle and start meditation nor he questioned from the very first moment from other teachers. He tried patiently. And once he understood that this is not he was looking for, he left. He did this several times. Finally he decided to search it by himself and arrived at his enlightenment. </p>
 254: <p>The <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.026.than.html">Ariyapariyesana Sutta: The Noble Search</a> is a partial description of his quest for enlightenment.</p>

<p>It contains passages like the following,</p>

<blockquote>
  <p>"Having thus gone forth in search of what might be skillful, seeking
  the unexcelled state of sublime peace, I went to Alara Kalama and, on
  arrival, said to him: 'Friend Kalama, I want to practice in this
  doctrine &amp; discipline.'</p>
  
  <p>"When this was said, he replied to me, 'You may stay here, my friend.
  This doctrine is such that a wise person can soon enter &amp; dwell in his
  own teacher's knowledge, having realized it for himself through direct
  knowledge.'</p>
  
  <p>"It was not long before I quickly learned the doctrine. As far as mere
  lip-reciting &amp; repetition, I could speak the words of knowledge, the
  words of the elders, and I could affirm that I knew &amp; saw — I, along
  with others.</p>
  
  <p>"I thought: 'It isn't through mere conviction alone that Alara Kalama
  declares, "I have entered &amp; dwell in this Dhamma, having realized it
  for myself through direct knowledge." Certainly he dwells knowing &amp;
  seeing this Dhamma.' So I went to him and said, 'To what extent do you
  declare that you have entered &amp; dwell in this Dhamma?' When this was
  said, he declared the dimension of nothingness.</p>
  
  <p>"I thought: 'Not only does Alara Kalama have conviction, persistence,
  mindfulness, concentration, &amp; discernment. I, too, have conviction,
  persistence, mindfulness, concentration, &amp; discernment. What if I were
  to endeavor to realize for myself the Dhamma that Alara Kalama
  declares he has entered &amp; dwells in, having realized it for himself
  through direct knowledge.' So it was not long before I quickly entered
  &amp; dwelled in that Dhamma, having realized it for myself through direct
  knowledge. I went to him and said, 'Friend Kalama, is this the extent
  to which you have entered &amp; dwell in this Dhamma, having realized it
  for yourself through direct knowledge?'</p>
  
  <p>"'Yes, my friend...'</p>
  
  <p>"'This, friend, is the extent to which I, too, have entered &amp; dwell in
  this Dhamma, having realized it for myself through direct knowledge.'</p>
  
  <p>"'It is a gain for us, my friend, a great gain for us, that we have
  such a companion in the holy life. So the Dhamma I declare I have
  entered &amp; dwell in, having realized it for myself through direct
  knowledge, is the Dhamma you declare you have entered &amp; dwell in,
  having realized it for yourself through direct knowledge. And the
  Dhamma you declare you have entered &amp; dwell in, having realized it for
  yourself through direct knowledge, is the Dhamma I declare I have
  entered &amp; dwell in, having realized it for myself through direct
  knowledge. The Dhamma I know is the Dhamma you know; the Dhamma you
  know is the Dhamma I know. As I am, so are you; as you are, so am I.
  Come friend, let us now lead this community together.'</p>
  
  <p>"In this way did Alara Kalama, my teacher, place me, his pupil, on the
  same level with himself and pay me great honor. But the thought
  occurred to me, 'This Dhamma leads not to disenchantment, to
  dispassion, to cessation, to stilling, to direct knowledge, to
  Awakening, nor to Unbinding, but only to reappearance in the dimension
  of nothingness.' So, dissatisfied with that Dhamma, I left.</p>
  
  <p>"In search of what might be skillful, seeking the unexcelled state of
  sublime peace, I went to Uddaka Ramaputta and, on arrival, etc.</p>
</blockquote>

<p>In other words he studied with various teachers, and successfully learned what they were teaching, but wasn't satisfied (and therefore went to another teacher, etc.).</p>

<hr>

<blockquote>
  <p>In other words, did Siddhartha Gautama arrive at his Enlightenment by BELIEVING in prevailing religious mythology and principles, or did he arrive at his Enlightenment by QUESTIONING, EXAMINING and REJECTING them?</p>
</blockquote>

<p>I think he started by learning teachers' doctrines and practices, but (having understood them) finding them unsatisfactory.</p>
 111: <p>There's no belief for a Buddha. A Buddha is omniscient. He knows what is right and what is wrong by direct knowledge.</p>

<p>Yes, the Buddha did uphold certain religious practices of the time which are congenial to the path.</p>

<p>ex: The five precepts, <a href="https://en.wikipedia.org/wiki/Dhutanga">13 Dutangas</a>, attainment of the Janas</p>

<p>He also rejected many false views which the contemporary religions were based on. They are grouped into 62 in <a href="http://www.accesstoinsight.org/tipitaka/dn/dn.01.0.bodh.html">Brahmajāla sutta</a>.</p>
