The first three rulers of the Ottoman realm were titled Bey. The chief sovereign of the Ottoman Empire only came to be called sultan starting in 1383 when Murad I was granted this title by the shadow caliph in Cairo.
The Ottoman state had started out as one of a dozen Turkish Ghazi Beyliks, roughly comparable to western European duchies, into which Anatolia (i.e., Asian Turkey, or Asia Minor) had been divided after the break-up of the Seljuk Sultanate of Ikonion (Konya) and the military demise of the Byzantine Empire. Its capital was Bursa. By 1336 it had annexed only the Beylik of Karasy, its western neighbour on the coast of the Sea of Marmara, but it began to expand quite rapidly thereafter.
As the Ottoman realm grew from a Beylik into an imperial sultanate, the title "Bey" came to be applied to subordinate military and administrative officers, such as a district administrator and lower-level minor military governors. The latter were usually titled sanjakbey (after the term "Sanjak", denoting a military horsetail banner). Beys were lower in rank than pashas and provincial governors (wālis, usually holding the title of pasha), who governed most of the Ottoman vilayets (provinces), but higher than effendis.
Over time the title became somewhat devalued, as Bey was even used as a courtesy title (alongside Pashazade) for a pasha's son. It also came to be attached to officers and dignitaries below those entitled to be pashas, notably the following military officer ranks (still lower ranks were styled efendi):
Oddly, the compound Beyefendi was part of the title of the husband (full style Damad-i-Shahyari (given name) Beyefendi) and sons (full style Sultanzade (given name) Beyefendi) of an Imperial Princess, and their sons in turn were entitled to the courtesy title Beyzade (literally "Son of a Bey". For the grandsons of an imperial princess, the official style was simply Bey after the name.).
By the late 19th century, "Bey" had been reduced in Ottoman Turkey to an honorary equivalent of the English-speaking address (not the British courtesy title) "Sir", somewhat akin to the contemporary Cockney usage of "guv'nor." While in Qazaq and other Central Asian Turkic languages, бай [baj] remains a rather honorific title, in modern Turkish, and in Azerbaijan, the word "bey" (or "bay") simply means "mister" (compare efendi) or "sir" and is used in the meaning of "chieftain" only in historical context. Bay is also used in Turkish in combined form for certain military ranks, e.g. albay, meaning colonel, from alay "regiment" and -bay, and yarbay, meaning lieutenant colonel, from yardim "assistance" and -bay (thus an "assistant albay").
As with most Turkish titles, it follows the name rather than precedes it as in western languages, e.g. "Ahmet Bey" for "Mr. Ahmet". When one speaks of Mr. Ahmet, the title has to be written with a capital (Ahmet Bey), but when one addresses him directly it is simply written without capital (Ahmet bey). Bey may combine with efendi to give a common form of address, to which the possessive suffix -(i)m is usually added: beyefendim, efendim.
Beyefendi has its feminine counterpart: hanımefendi , used alone, to address a woman without her first name. And with the first name: Ayşe Hanım or Ayşe hanım, for example, according to the rule given above about the use of the capital letter.
Skanderbeg was a famous Albanian with the Beg title.
The term is not used anymore in Albania except when referring to historical figures and events or for humorous purposes (meaning to joke about someone who does not possess a clear thinking ability). Nevertheless, a select number of families still use the bey-ending in their last names. It is often cited as tribute to past blood lines. However, the name is generally associated with the Çabej line of Albania.
The title Bey (Arabic: باي) could be maintained as a similar office within Arab states that broke away from the High Porte, such as Egypt and Sudan under the Muhammad Ali Dynasty, where it was a rank below pasha (maintained in two rank classes after 1922), and a title of courtesy for a pasha's son.
Even much earlier, the virtual sovereign's title in Barbaresque North African 'regency' states was "Bey" (compare Dey). Notably in Tunis, the Husainid Dynasty used a whole series of title and styles including Bey:
In the Mani Peninsula, in times of the Ottoman conquest of Greece, the de facto sovereign country of the Maniots in the southern Peloponnesus, had as head of state a chieftain which combined both military command and judiciary activities who was entitled as Bey following the Turkish influence over conquered areas, especially in the Balkans. It was usual to add the title to their own given names, therefore the most renowned Bey of Mani, Petros Mavromichalis was simply known as Petrobey.
Other Beys saw their own Beylik promoted to statehood, e.g.:
Bey or a variation has also been used as an aristocratic title in various Turkic states, such as Bäk in the Tatar Khanate of Kazan, in charge of a Beylik called Bäklek. The Balkar princes in the North Caucasus highlands were known as taubiy (taubey), meaning the "mountainous chief".
Sometimes a Bey was a territorial vassal within a khanate, as in each of the three zuzes under the Khan of the Kazakhs.
The variation Beg, Baig or Bai, is still used as a family name or a part of a name in South and Central Asia as well as the Balkans. In Slavic-influenced names, it can be seen in conjunction with the Slavic -ov/-ović/ev suffixes meaning "son of", such as in Izetbegović, Abai Kunanbaev (Abai Kunanbaiuli).
The word entered English from Turkish bey, and the Turkish word has its origins in Old Turkic beg. There are different theories about the further etymology of the word beg. According to one theory the word may ultimately come from Middle Chinese baak, pak. Another theory states that the word may have its origins in Sogdian baga. Gerhard Doerfer pointed out the possibility that the word is genuinely Turkic.