Allah! There is no god but He. (Quran 2:255)
The Quran calls Allah the Lord of the Worlds. We know and understand Allah through His names, and attributes. These include the Creator, the King, the One, the Only and the All-Seer.
Two of Allah’s most important names occur in a phrase that prefaces all but one chapter of the Quran, Bismillah, Ar Rahman, Ar Raheem (In the name of Allah, the Most Compassionate, the Most Merciful). However, the greatest and most sublime name is the name Allah.
Dictionary.com defines the word Allah as, the Supreme Being, God. When those whose first language is Arabic use the word Allah they are referring to God, regardless of their religious affiliation.
For example Arabic Jews and Christians refer to God as Allah in exactly the same way that those whose first language is Italian refer to God as Dio. However the Arabic word Allah contains a more in-depth description of what God is.
Allah is God, the Creator, and Sustainer of the world. Nothing is similar to Him and nothing is comparable to Him. When Prophet Muhammad was asked by his companions about Allah, the answer came directly from God Himself. Chapter 112 was revealed.
Say (O Muhammad): He is Allah, [who is] One. Allah, the Self-Sufficient Master. He begets not, nor was He begotten; and there is none co-equal or comparable to Him.
And throughout the Quran, God, Allah, describes Himself to us.
… There is nothing like Him… (Quran 42:11)
And there is none co-equal or comparable to Him. (Quran 112:4)
He is the First (nothing is before Him) and the Last (nothing is after Him), the Most High (nothing is above Him) and the Most Near (nothing is nearer than Him). And He is the All-Knower of everything. (Quran 57:3)
In the Arabic language, the word Allah stands alone. While the English word God can be made plural, as in gods, the Arabic word cannot. The English word God is able to change gender, as in goddess, but the word Allah is genderless.
The use of the words He or Him are grammatical only and do not indicate that Allah has any form of gender comprehensible to us. Allah is unique and in the Arabic language so too is His name.
Verily! I am Allah! None has the right to be worshiped but I, so worship Me… (Quran 20:14)
Thus using the word Allah indicates that God is the one who is worshiped and the one who deserves to be worshiped by the whole of His creation.
Sheikh Uthaymeen (1929 – 2001 CE) defined the word Allah as follows:
“The word “Allah” is a proper noun referring to the Lord. Its root is the word al-Ilaah (“the God”), but the word is contracted to make it easier to pronounce, because it is repeated so frequently. The word ilaah refers to the one who is loved, and the one who is loved is the one who is worshiped out of love and veneration.”
The Name Allah is mentioned in the Quran more often than any other name by which Allah refers to Himself. It is mentioned 2602 times.
Let us compare this to other names that are frequently mentioned in Quran and used by the believers in their supplications.
Ar Raheem (the Most Merciful) is mentioned 114 times and Ar Rahman (the Most Compassionate) is mentioned fifty seven times. There is a vast difference, and it is obvious that Allah has specifically given this name a special status.
Prophet Muhammad told us on many occasions that God’s greatest name is Allah.
Prophet Muhammad heard a man supplicating:
“Oh God, I ask you by the fact that you are God, there is no god except You, the One, the Self-sufficient Master, You not beget nor were you begotten, and there is none comparable to You”.
He said, to the man:
You have supplicated to God using His Greatest Name, when asked with this name He gives, and when supplicated by this name He answers.
At another time Prophet Muhammad said:
The Greatest name of Allah is in these two verses: ‘And Your Allah is One Allah. There is no deity worthy of worship except Him, the Beneficent, the Merciful’ (Quran 2:163) and also in the opening of Al Imran, ‘Alif – Lam – Meem. Allah! There is no deity worthy of worship except Him. The Living, the Sustainer.’ (Quran 3:1-2)
Prominent Egyptian scholar, Sheikh Ahmad ash-Sharbaasi said:
“Allah is the Name, which is unique for the Truth, Glorified is He and He is singled out Himself for it. He has made it the first of His Names and added all the other Names to it and has not added it to any other name. Everything, therefore, that comes after it is a description and attribute of it.”
Allah is the greatest name because it encompasses all of God’s names and attributes. Their meanings are incorporated in the name Allah. They are signs by which we recognize the wonder and glory of God – Allah. The essence of all the names and attributes are unified in this one name, Allah, which denotes His ultimate perfection.
In conclusion understanding that Allah is the greatest name of all is a very good place to start when making a study of the innumerable names of God.
Using God’s names in all of our supplications strengthens our belief because the more we understand God the closer we feel to Him.
Consequently, feeling close to God makes us determined to worship Him in a way that is pleasing to Him.
One of Islam’s most respected scholars, Ibn al-Qayyim, said:
“The key to the call of the Messengers, (and) the essence of their Message, is knowing Allah through His Names, His Attributes, and His Actions, because this is the foundation on which the rest of the Message, from beginning to end, is built.” 
The most beautiful names belong to Allah, so call on Him by them. (Quran 7:180)
 Abu Dawood, At Tirmidhi.
Al-Sawaaiq al-Mursalah `Ala al-Jahmayyah wal-Muattilah.