Albert Barnes Commentary Ezra 7:12

"Artaxerxes, king of kings, unto Ezra the priest, the scribe of the law of the God of heaven, perfect and so forth." — Ezra 7:12 (ASV)

The title, “king of kings,” is assumed by almost all the Persian monarchs in their inscriptions.

Perfect peace - “Peace” is not in the original, and the word translated “perfect” occurs only in this place. Some prefer to take it as an adjective descriptive of Ezra (see margin); others (Septuagint) as the opening word of the first paragraph of the letter, and give it the meaning, “it is completed.”