The author of the Holy Quran is none other than Allah Almighty, God. He revealed the Book to the Prophet Muhammad (peace be upon him), through Archangel Gabriel, over a period of 23 years.
According to Wikipedia: ‘Allah’ is the Arabic word for God in Abrahamic religions. According to the British Oxford Dictionary: ‘Allah’ is the name of God among Muslims. However, the most accurate definition of the word ‘Allah’ is the one that’s mentioned in the Holy Quran:
Holy Quran; Surah 112; Verses 1-4:
1. قُلْ هُوَ اللَّـهُ أَحَدٌ
Say: He is God the One and Only;
2. اللَّـهُ الصَّمَدُ
God the Eternal Absolute;
3. لَمْ يَلِدْ وَلَمْ يُولَدْ
He begetteth not nor is He begotten;
4. وَلَمْ يَكُن لَّهُ كُفُوًا أَحَدٌ
And there is none like unto Him.
God Almighty himself clarifies that the Quran is the revelation and word of God, and that there is truly no other being that can produce anything like it:
Holy Quran; Surah 46; Verse 2:
2. تَنزِيلُ الْكِتَابِ مِنَ اللَّـهِ الْعَزِيزِ الْحَكِيمِ
The revelation of the Book is from God the Exalted in Power Full of Wisdom.
Holy Quran; Surah 26; Verse 192-19:
192. وَإِنَّهُ لَتَنزِيلُ رَبِّ الْعَالَمِينَ
Verily this is a Revelation from the Lord of the Worlds:
193. نَزَلَ بِهِ الرُّوحُ الْأَمِينُ
With it came down the Spirit of Faith and Truth
194. عَلَىٰ قَلْبِكَ لِتَكُونَ مِنَ الْمُنذِرِينَ
To thy heart and mind that thou mayest admonish
195. بِلِسَانٍ عَرَبِيٍّ مُّبِينٍ
In the perspicuous Arabic tongue.
196. وَإِنَّهُ لَفِي زُبُرِ الْأَوَّلِينَ
Without doubt it is (announced) in the mystic Books of former peoples.
Holy Quran; Surah 2; Verse 23:
23. وَإِن كُنتُمْ فِي رَيْبٍ مِّمَّا نَزَّلْنَا عَلَىٰ عَبْدِنَا فَأْتُوا بِسُورَةٍ مِّن مِّثْلِهِ وَادْعُوا شُهَدَاءَكُم مِّن دُونِ اللَّـهِ إِن كُنتُمْ صَادِقِينَ
And if ye are in doubt as to what We have revealed from time to time to Our servant then produce a Surah like thereunto; and call your witnesses or helpers (if there are any) besides God if your (doubts) are true.
24. فَإِن لَّمْ تَفْعَلُوا وَلَن تَفْعَلُوا فَاتَّقُوا النَّارَ الَّتِي وَقُودُهَا النَّاسُ وَالْحِجَارَةُ ۖ أُعِدَّتْ لِلْكَافِرِينَ
But if ye cannot and of a surety ye cannot then fear the fire whose fuel is Men and Stones which is prepared for those who reject Faith.