I have translated Al-'Aql as "intelligence" for lack of a better word, but the actual meaning is related but quite different.  Allah Most High said:

{Kadhaalika yubayyinu Allahu lakum aayaatihi la'allakum ta'qiloon.}
{Thus Allah makes clear to you His signs that perchance you may understand.}  Al-Baqarah: 242

From this, we see that 'Aql is not simply some innate ability with which people are born.  If Allah's making His signs clear to us can induce 'Aql, then clearly it is more than that.
Linguistically, the meaning of 'Aql is: restricting/controlling or prohibiting.  It got this name because 'Aql is that which prevents one from comitting ugly deeds which are at odds with it.  Technically, the meaning of 'Aql is: a word which describes knowledge of what is right and what is error and should be avoided.

The stages or levels of 'Aql are as follows:

• Adeeb (well-mannered).  One whose sense or intelligence keeps them within the bounds of Islamic adab - manners or etiquette. 
• Areeb (capable).  One who is skillful and resourceful.  Not only well-mannered but able to help others and accomplish Islamic solutions to Muslims' problems.
• Labeeb (intelligent).  One who is sensible, reasonable and blessed with deep and sound understanding.
• 'Aaqil (discerning).  One who is truly blessed with understanding as well as restraint.  One who is judicious and wise whose sound understanding of what is right and what is wrong keeps them away from all unseemingly statements and deeds.

As you can see, the entire concept of 'aql or "intelligence" is quite different in the Islamic understanding than in western culture.  "Intelligence" in English could be best described as the second level above with or without the first one.  If you can solve problems, build things or do any number of other things, you are regarded as "intelligent".  Good behavior and restraint are not really considered PART of "intelligence" in this culture.

The concept of 'aql is also itself divided into two types:

1. Ghareeziy (innate or natural).  This is that faculty which Allah has placed in human beings which distinguishes them from the animals.  It is that which brings on takleef (responsibility) of the individual before Allah for their actions.  It is absent (permanently or temporarily) from one who is insane, asleep or unconscious.
2. Muktasab (acquired).  This is the one which bears fruit and is the one referred to in the verse quoted earlier:
   
   {Kadhaalika yubayyinu Allahu lakum aayaatihi la'allakum ta'qiloon.}
   {Thus Allah makes clear to you His signs that perchance you may understand.}  Al-Baqarah: 242
   
   It increases with study, learning and remembrance of Allah by Allah's permission.  This is the one which holds one back from ugly deeds and guides one to noble deeds.

So, 'aql contains part of the meaning off "intelligence" in English.  The remaining part of "intelligence" is that reasoning or thinking which fails to lead one to what is right or leads one astray.  We also call this "intelligence", but it is not called 'aql.  Rather Allah calls this hawaa (usually translated "lusts" or "desires").

'Aql can be acquired, cultivated and increased by pondering Allah's signs both in his creation and in His Book.  Allah said:

{Alladhina yadhkuroona Allaha qiyaaman wa qu'oodan wa 'alaa junoobihim wa yatafakkaroona fiy khalqi as-samaawaati wa al-ardhi.  Rabbanaa maa khalaqta hadhaa baatilan subhaanaka fa qinaa 'adhaaba an-naari.}
{Those who mention Allah standing, sitting and on their sides and who ponder the creation of the heavens and the earth.  Lord!  You did not create this for nothing.  Exalted are You so protect us from the punishment of the fire.}  Aal-'Imraan: 191

Pondering of Allah's creation - for those blessed with true "intelligence" - will inevitably lead to exalting Allah, worshipping Him and seeking his pleasure, mercy and protection.  The signs show us that Allah did not create all that we see and don't see without point.  Rather, He created them as pointers and proofs of His wisdom and His power and created the earth as a place off testing for His slaves so that those who obey Him would be separated from those who rebel.

Knowledge is essential for acquiring useful "intelligence" ('aql).  Those who "know", those who pursue knowledge and aqcuire it from wherever it is available are the ones who will be able to understand that which they need to understand.  Allah said:

{Wa tilka al-amthaalu nadhribuhaa li an-naasi wa maa ya'qiluhaa illa al-'aalimoon.}
{And those are the similitudes we present to the people and none comprehend it but the knowledgeable.}  Al-'Ankaboot: 43

There is no benefit in "intelligence" which is not 'aql, i.e., which does not restrain one from ugly deeds nor guide one to acts of obedience.  Just as there is no benefit in much "knowledge" which people acquire.  The Prophet (sas) sought refuge in Allah from 'ilmin laa yanfa'u (knowledge which is of no benefit).  He (sas) also distinguished between the two meangings (i.e., intelligence which is 'aql and intelligence which is not) in the following hadith:

"Al-kayyis man daana nafsahu wa 'amila limaa ba'ada al-mauti wa al-'aajiz man atba'a nafsahu hawaahu wa tamannaa 'alaa Allahi al-amaaniy."
"The kayyis (another word meaning one with 'aql) is the one who takes himself to account and bases his actions on what comes after death.  The incapable is the one who causes his self to follow his inclinations and gives himself false hopes about Allah."  At-Tirmidhiy

Aisha (ra) said:  "Whoever Allah granted 'aql has succeeded."

This Ummah needs at all time not only people of sound intelligence and reasoning, but also those who go even deeper and who can guide the Ummah to what is best like the way the four khulafaa and others did. Umar (ra) said: 

"Laisa al-'aaqil man ya'rifu al-khaira min ash-sharri wa lakinnahu alladhiy ya'rifu khaira ash-sharrain."
"The 'aaqil is not the one who knows good from evil, rather he is the one who knows the better (i.e., "lesser") of two evils."

Ibn Mubaarak was asked:  "What is the best thing which a man can be given?"  He answered:  "Sound intelligence."  It was said:  "And, if not that?"  He answered:  "Good manners."  It was said:  "And, if not that?"  He answered:  "A righteous brother from whom to get advice and guidance."  It was said:  "And, if not that?"  He answered:  "Keeping quiet for a long time."  It was said:  "And, if not that?"  He answered:  "Quick death."