The Affirmer of Truth, The Guarantor, The Giver of Faith.
The name of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ as Al-Mu'min (in Arabic: ٱلْمُؤْمِنُ) means The One who witnessed for Himself that no one is God but Him. And He is the one who sent down Messengers and revealed His Books as clear proofs.