A lancer was a type of cavalryman who fought with a lance. Lances were used for mounted warfare in Assyria as early as 700 BC and subsequently by India, Egypt, China, Persia, Greece, and Rome. The weapon was widely used throughout Eurasia during the Middle Ages and the Renaissance by heavy cavalry, but fell out of general use by the late 16th century, before its revival by light cavalry in the early 19th century.

Historically, cavalry are soldiers or warriors who fight mounted on horseback. Until the 20th century cavalry were the most mobile of the combat arms, operating as light cavalry in the roles of reconnaissance, screening, and skirmishing in many armies, or as heavy cavalry for decisive shock attacks in other armies. An individual soldier in the cavalry is known by a number of designations depending on era and tactics, such as a cavalryman, horseman, trooper, cataphract, knight, drabant, hussar, uhlan, mamluk, cuirassier, lancer, dragoon, or horse archer. The designation of cavalry was not usually given to any military forces that used other animals for mounts, such as camels or elephants. Infantry who moved on horseback, but dismounted to fight on foot, were known in the early 17th to the early 18th century as dragoons, a class of mounted infantry which in most armies later evolved into standard cavalry while retaining their historic designation.