Mister, usually written in its contracted form Mr. (American English) or Mr (British English), is a commonly used English honorific for men without a higher honorific, or professional title, or any of various designations of office. The title Mr derived from earlier forms of master, as the equivalent female titles Mrs, Miss, and Ms all derived from earlier forms of mistress. Master is sometimes still used as an honorific for boys and young men. The plural form is Messrs(.), derived from the French title messieurs in the 18th century.
https://en.wikipedia.org/wiki/Mr.