Who is Allah?
This question is best answered by the God Himself.
1. Say, "He is Allah , [who is] One,
2. Allah , the Eternal Refuge,
3. He neither begets nor is born,
4. Nor is there to Him any equivalent."  [The Quran 112]

Allah is the only true God who deserves to be worshipped alone and who has no coequal in Himself as well  as  in  His  Names  and  Attributes.  
legacy.quran.com/3/18

Allah The Creator has Perfect Attributes. He is the First, nothing is before Him.  He is the Last, everything ends except Him; the Most High, nothing is above Him; the Most Near, nothing is beyond His reach and his compassing, and He is the Most High in His nearness..

http://legacy.quran.com/57/3

God alone is the Almighty, the Creator, the Sovereign, and the Sustainer of everything in the whole universe.  He manages all affairs.  He stands in need of none of His creatures, and all His creatures depend on Him for all that they need.

God is not a trinity.  God has said in the Quran:

 Indeed, they disbelieve who say, “God is the third of three (in a trinity),” when there is no god but one God.  If they desist not from what they say, truly, a painful punishment will befall the disbelievers among them. Would they not rather repent to God and ask His forgiveness?  For God is Oft-Forgiving, Most Merciful.  The Messiah (Jesus), son of Mary, was no more than a messenger...  (Quran, 5:73-75)

Islam rejects that God rested on the seventh day of the creation, that He wrestled with one of His angels, that He is an envious plotter against mankind, or that He is incarnate in any human being.  Islam also rejects the attribution of any human form to God. All of these are considered blasphemous.  God is the Exalted.  He is far removed from every imperfection.  He never becomes weary.  He does not become drowsy nor does he sleep.
http://legacy.quran.com/5/73-75

All the attributes of Sovereignty reside in God alone.  He alone possesses all the attributes of Divinity.  God is unique and dissimilar to anything.
legacy.quran.com/42/11

God is the All-Hearing, the All-Seeing, and the All-Knowing.  In a perfect manner, His knowledge encompasses all things, the open and the secret, and the public and the private.  He knows what has happened, what will happen, and how it will happen. 
legacy.quran.com/24/64

Allah did not leave us aimless. He set a code to live accordingly. So He legislates, commands, and prohibits, and  justly  sets reward  and accountability, because He is all-Just.  
legacy.quran.com/40/62