Dux (plural: duces) is Latin for leader (from the verb ducere, 'to lead') and later for Duke and its variant forms (Doge, Duce, etc.).

During the Roman Republic, dux could refer to anyone who commanded troops, including foreign leaders, but was not a formal military rank. In writing his commentaries on the Gallic Wars, Julius Caesar uses the term only for Celtic generals, with one exception for a Roman commander who held no official rank.

Until the third century AD, dux was not a formal expression of rank within the Roman military or administrative hierarchy.

In the Roman military, a Dux would be a general in charge of two or more legions. While the title of Dux could refer to a consul or imperator, it usually refers to the Roman governor of the provinces. As the governor, the Dux was both the highest civil official as well as the commander-in-chief of the legions garrisoned within the province.

However, during the time of the Dominate, the powers of a Dux were split from the role of the governor and were given to a new office called "Dux". The Dux was still the highest military office within the province and commanded the legions, but the governor had to authorize the use of the Dux's powers. But once authorized, the Dux could act independently from the governor and handled all military matters. An example would be the Dux per Gallia Belgica who was the Dux of the province of Gallia Belgica.

Benito Amilcare Andrea Mussolini (Italian pronunciation: [beˈniːto musːoˈliːni]; 29 July 1883 – 28 April 1945) was an Italian politician who led the National Fascist Party, ruling the country from 1922 to his ousting in 1943, and is credited with being one of the key figures in the creation of fascism.

Originally a member of the Italian Socialist Party and editor of the Avanti! from 1912 to 1914, Mussolini fought in World War I as an ardent nationalist and created the Fasci di Combattimento in 1919, catalyzing his nationalist and socialist beliefs in the Fascist Manifesto, published in 1921. Following the March on Rome in October 1922 he became the 27th Prime Minister of Italy and began using the title Il Duce by 1925, about which time he had established dictatorial authority by both legal and extraordinary means, aspiring to create a totalitarian state. After 1936, his official title was Sua Eccellenza Benito Mussolini, Capo del Governo, Duce del Fascismo e Fondatore dell'Impero ("His Excellency Benito Mussolini, Head of Government, Duce of Fascism, and Founder of the Empire") Mussolini also created and held the supreme military rank of First Marshal of the Empire along with King Victor Emmanuel III, which gave him and the King joint supreme control over the military of Italy. Mussolini remained in power until he was replaced in 1943; for a short period after this until his death, he was the leader of the Italian Social Republic.