"Not equal are those of the believers who stay home without any proper excuse and those who strive hard and fight in the cause of Allah with their wealth and their lives." — The Qur'an, 4:95
First introduced by the caliph al-Muwaffaqin the late 9th century CE, the Mamluks were thought to have been the result of attempts to reform the ghilman system of military slavery which was increasingly prevalent throughout the Islamic Middle East - the term "mamluk" already is derived from the Arabic word for "owned" or "property" - in other words, the property of a sultan or king (in Arabic, "malik"). Mamluks were used to bypass the need for a sultan to rely on the local nobility for military manpower, as many a caliph felt that local noblemen could not be trusted.
Ostensibly the most powerful cavalry unit in the Muslim arsenal, Mamluk Lancers are known for one thing, and one thing only: the ability to lay waste to the unwary wholesale, for they are some of the best cavalry units that the Islamic world has ever seen. Although they don't have the same level of armour as European Men-at-Arms do, they have a faster and more ferocious attack, with an added attack bonus, making them highly dangerous opponents. The only problem however is in their cost - which is fairly exorbitant in wealth - and the fact that they are recruitable only if you have researched both Darul Islam and Monarchy. Plus, being recruitable only from the Nobles' Court means that they aren't easily obtained and are only accessible to the most warlike of all factions.
By the 13th century, the Mamluks formed a military caste very similar to Christian knights in which while being de jure slaves, they exercised extensive power over politics through the dependence of Islamic monarchies on them, and while owing nominal allegiance to Baghdad, ruled supreme in their juristidctions, eventually forming Mamluk dynasties such as those of Egypt. The most famous of the mamluks was Baibars, the Bahrid sultan who was the hero of Ain Jalut in 1260.