Commander

Commanders are the heart and soul of units. If a commander dies, their whole unit is lost permanently. They are invulnerable so long as at least one soldier is under their command. Even if all soldiers under a commander die in battle, they will be replenished on the next island or after replenishing in a house. As such, make sure that your commanders always survive!

Commanders may flee with their surviving soldiers by clicking on the skill and then on an empty boat on the beach. The boat must be big enough to carry all the units alive in order to flee. Archers can still fire at and from a fleeing boat.

New commanders can be recruited on islands that have little banners under them, which indicates that the island is this commander's home island. Commanders cannot flee from their home islands; make sure to bring enough support to win the island if you want to recruit said commander! Note that you will only be allowed to bring up to three units of your own, instead of the usual four. The local commander will automatically be the 4th unit.

Most newly recruited Commanders come with a unit of Militia, though later in the game every commander will have a unit with a class already set, like Infantry, Pikes or Archers. The later the game gets, the higher the level the units are.

Commanders can be given items; choose wisely, as items cannot be removed once added to a unit.

Since Jotunn Edition, Commanders may now come with one of thirteen small, passive buffs, called Traits which can be distinguished from each other by the symbol on the Commander's banner.

Strengths

 * Always a melee unit, regardless of unit class they commands. As such it's possible that the Commander can kill units with their sword even when within a Pikes or Archers unit.
 * Can be granted items and that give advantages or new skills to units.
 * Increased health/knockback/stun resistance compared to individual soldiers.

Weaknesses

 * Always a melee unit, regardless of the unit class they command.
 * No shield, regardless of unit class they command.
 * They can be knocked down.
 * The rest of the unit cannot recover inside of houses without the Commander inside with them. If the Commander is separated from his unit while performing a Replenish and is killed the unit is considered killed.

Trivia

 * Before the Jotunn Edition update, each Commander had their own flag with a unique shape and pattern. This was 100% cosmetic.
 * Before Jotunn Edition each Commander had their own coins with which to upgrade the unit.

Link
* Source: http://badnorth.wikidot.com/commander