Jehovah
I the LORD have spoken it: it shall come to pass, and I will do it; I will not go back, neither will I spare, neither will I repent; according to thy ways, and according to thy doings, shall they judge thee, saith the Lord GOD. Ezekiel 24:14
The LORD (Jehovah) speaks in the first person and promises His word will be fulfilled. Latter-day Saints understand Jehovah to be the premortal Jesus Christ, whose word never fails.
How we know: Jehovah is the premortal Christ (Abraham 1:16; D&C 110:3–4)
