Jehovah
Jehovah (LORD) — "I AM", the covenant God of Israel
For I am the LORD: I will speak, and the word that I shall speak shall come to pass; it shall be no more prolonged: for in your days, O rebellious house, will I say the word, and will perform it, saith the Lord GOD. Ezekiel 12:25–28
People mocked Ezekiel's prophecies as always failing or being about the far future. Jehovah, the premortal Christ, answers with His own name: because He is the LORD, every word He speaks will be fulfilled.
AttestedJehovah — the LORDHe speaks in the first person
How we know: the verse itself names Him