1. linguistic typology

Mister, usually written in its abbreviated form Mr. (US) or Mr (UK), is a commonly-used English honorific for men. The title derived from earlier forms of master, as the equivalent female titles Mrs, Miss and Ms all derived from earlier forms of mistress. 
Historically, mister – like Sir or my lord – was applied only to those above one's own status in the peerage. This understanding is now obsolete, as it was gradually expanded as a mark of respect to those of equal status and then to all gentlemen. It is now used indiscriminately.
In past centuries, Mr. was used with a first name to distinguish among family members who might otherwise be confused in conversation: Mr. Doe would be the eldest present; younger brothers or cousins were then referred to as Mr Richard Doe and Mr William Doe and so on. Such usage survived longer in family-owned business or when domestic servants were referring to adult male family members with the same surname: "Mr Robert and Mr Richard will be out this evening, but Mr Edward is dining in," but such usage today is rare in American culture but still quite common in others as a sign of respect when first names are being used, the last name is not known, or where English is not the
mother tongue.
Professional titles, Mr. is sometimes combined with certain titles (Mr. President, Mr. Speaker, Mr. Justice, Mr. Dean). The feminine equivalent is Madam. All of these except Mr. Justice are used in direct address and without the name. The title Mr. Justice is not used in direct address. In certain professional contexts in different regions, Mr has specific meanings; the following are some examples.
In Medicine, in the United Kingdom, the Republic of Ireland and in some Commonwealth countries (such as South Africa), many surgeons use the title Mr (or Miss, Ms, Mrs, as appropriate), rather than Dr (Doctor). Until the 19th century, earning a medical degree was not required to become a qualified surgeon. Hence the modern practice of reverting from Dr back to Mr after successfully completing qualifying exams in surgery (e.g. Memberships of the Royal College of Surgeons) is a historical reference to the origins of surgery in the United Kingdom as non-medically qualified barber surgeons.