Enemy Units refer to the units that the CPU (or multiplayer opponent) controls directly. Enemy units can come in a variety of classes, but generally the most commonly seen enemy classes are Knights, Paladins, Wyvern Riders, Brigands, and Soldiers with the last two disappearing later in the game. Some enemy units can be recruited to become Player Units (e.g. Joshua, Jamke, Aran). Enemy Units can only move during the Enemy Phase, which occurs directly after the Ally Phase. Enemy Units are usually represented by the color red; a red-colored HP bar, a red circle surrounding the unit, or red-colored clothing/hair. Enemy Units usually rely on sheer power through numbers and typically possess sub-par stats (with the exception of special enemies, recruitable enemies or boss characters). An enemy unit can be weak or strong, with the strongest usually being bosses, final bosses and endgame enemies, and the weakest are usually early enemies and even some bosses and recruitable units can be weak. Some recruitable enemies (like Nabarl and Jill) are extremely powerful and make some of the best units in your army. In Fire Emblem: Radiant Dawn and Fire Emblem: Path of Radiance, the enemy phase comes after the player phase and then directly after the ally phase, it also comes before the other phase. In the beginning of a game, the enemy units usually use weak weapons like Iron Swords, Iron Axes, Iron Lances, etc., while magic users usually have weak magic spells, like fire, lightning, wind, etc. As the game progresses however, their weapons and stats improve greatly. Additionally, in Radiant Dawn, enemy units can gain weapon levels during chapters, which, in the case of laguz units, may make them dangerously more powerful. There are also gliches that allow you to control enemies units.
For some reason, the enemy uses male sprites for all enemy units without a character portrait unless there is no other choice as with classes like Pegasus Knight and Valkyrie. The main exception to this is the fourth and fifth game where generic enemy units such as Heroes, Mage Fighters, and Wyvern Riders would sometimes be female.