It's scripture.Three times Jesus identifies Himself this way. Don't be dubious about God's Word.
Rev 1:8 I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty.
Rev 1:11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea.
Rev 22:12 And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be. Rev 22:13 I am Alpha and Omega, the beginning and the end, the first and the last.