The Essence
Al-Aakhir is the Last. When the universe and everything within it comes to an absolute end, He alone will remain. He is the ultimate destination to whom everything returns.
In the Quran
هُوَ الْأَوَّلُ وَالْآخِرُ
"He is the First and the Last (Al-Aakhir)... (Surah Al-Hadid 57:3)"
In Your Duas
وَأَنْتَ الآخِرُ فَلَيْسَ بَعْدَكَ شَىْءٌ
"And You are the Last, there is nothing after You."
— Sahih Muslim 2713