Brigadier brɪɡəˈdɪər is a military rank, the seniority of which depends on the country. In some countries, it is a senior rank above colonel, equivalent to a brigadier general or commodore, typically commanding a brigade of several thousand soldiers. In other countries, it is a non-commissioned rank.
The word and rank of "Brigadier" originates from France. In the French Army, the Brigadier des Armées du Roi (Brigadier of the King's Armies) was a general officer rank, created in 1657. It was an intermediate between the rank of Mestre de camp and that of Maréchal de camp.
The rank was first created in the cavalry at the instigation of Marshal Turenne on June 8, 1657, then in the infantry on March 17, 1668, and in the dragoons on April 15, 1672. In peacetime, the brigadier commanded his regiment and, in maneuvers or in wartime, he commanded two or three - or even four - regiments combined to form a brigade (including his own, but later the rank was also awarded to lieutenant-colonels, which allowed for the promotion of an officer who did not have his own regiment).
Before the rank of brigadier of the armies was dissolved in 1788, it was materialized by the wearing of a single star. And when it was abolished that year, the number of stars of its immediate superiors was not modified, which explains why today French generals have one more star on their insignia than their foreign counterparts (notably American).
Note that the rank of "Chef de brigade" created during the French Revolution replaced that of Colonel. A brigade commander then commanded... a half-brigade (a name that replaced the regiment).
The rank of Brigadier of the Armies reappeared during the Third Republic. It designates a colonel, experienced as a regimental commander, who has under his command several regiments without having the annexed units that would make this group a brigade. The army brigadier wears the colonel's uniform and insignia. The rank was definitively abolished in 1945.