Abram becomes Abraham; Sarai becomes Sarah
In Genesis 17, God makes his covenant with Abram and renames him: Abram (four Hebrew letters) becomes Abraham (five). The added letter is he. In the same chapter Sarai becomes Sarah, and again a he stands at the end of the new name. The text says plainly why the names change — "a father of a multitude of nations have I made thee" — and says nothing at all about the letters. But the letters really did change, at the exact moment the covenant was cut, and that is a fact you can see on the page.