John Gill Commentary 1 Kings 18:8

"And he answered him, It is I: go, tell thy lord, Behold, Elijah [is here]." — 1 Kings 18:8 (ASV)

And he answered him, I am He did not desire to be concealed, his orders were to show and make himself known to Ahab, and Obadiah was one of his domestic servants: go tell your lord, behold, Elijah is here ; in such a place, ready to face him at any time. Elijah, by calling Ahab the lord of Obadiah, as he tacitly reproves him for calling him lord, shows reverence to Ahab as a king, and yet that he was fearless of him, as he was the prophet and ambassador of the Lord of hosts to him.