Etymology
editMr. comes from Middle English, where it was the abbreviation of maister, meaning “master.” Master was the original preferred title for young unmarried men, and mister was specific to those who were married, until the former fell out of use and the latter came to apply to both https://www.merriam-webster.com/words-at-play/how-to-pluralize-mr-mrs-miss-honorifics-usage