With 1.19 update, the commanders have come in the game.
Commanders are unique characters who can boost your efficiency both in attack and defense.

There are several tags for commanders, such as:
+ Warrior: skills related to fleet attack, armor, speed when attacking other players.
Resource Collection: prioritize efficiency on wrecks resource collection.
+ Rally: when appointed as Head commander, it improves the whole group’s parameters
+ Defense: improves damage and armor of defending units.
+ Towers: improves damage and armor of tower units in defense.
+ Hunter: improves efficiency of pirates confrontations increasing wreck size, increases damage, armor and/or speed against pirates, and chance of finding crates.
+ Pathfinder: improves efficiency of pirates confrontations increasing debris collection and wreck spawn chance.
+ Support: these provide a bonus on leadership and extra experience gain.
With 1.21 update, there is a new type of Commanders called Advisors!
Advisors are civilian Commanders who do not take part in active combat missions or base defense operations. Their strengths contribute to increasing the efficiency of the base economy:
these Commanders need special working arrangements, and they’ve got one: the Office!
It is located in the Radar building. As you upgrade this building, the number of slots in the Office increases, and you can appoint Advisors there. Once they’re accommodated, their skills become active.
In addition, Advisors, like all other Commanders, can advance their leadership level, but in the case of our new Commanders, it works a little differently: with higher leadership, you get different passive bonuses (for example, boosting the JET recovery); hence, the higher the leadership, the better the bonus!

Commander’s level and leadership.
Commander’s level is increased by acquiring experience. This can be done by attacking regular pirates or applying expertise modules to them. Every 10 levels, the Commander needs to be ranked up to be able to achieve further levels, up to level 50. Expertise modules can be acquired by defeating regular pirates, activating summoning crystals or offered packs.

Leadership allows the commander to increase the maximum size of the fleet he commands. This is increased by applying management modules to him. Each module has a diminishing chance to success, increasing the leadership by 500 points on every success. Management modules can be acquired by defeating Elite Pirates level 6 and above, by activating summoning crystals, or by offered packs.

Rank and skills:
Rank - ranks are represented by stars. A commander can be promoted to the next rank (obtaining 1 more star) by first maxing the Commander’s level for the respective rank. Each rank allows a commander up to level 10 levels, so a one star commander has a maximum achievable level of 10, a rank 2 has a maximum level of 20, and so forth. Promoting a commander to the next rank, will unlock the respective skill to the obtained rank.
Skills - each commander has a specific set of 5 skills. These are unlocked when the commander is promoted:
Once unlocked, skills can be upgraded up to 5 levels. In order to do so, you need to have enough Commander badges to upgrade them. If more than one are unlocked and upgradable, the upgrade will be done to a random skill, not necessarily from lowest to highest ranked.

SPECIAL CONSIDERATIONS:
It is worth to note that regarding commander’s PvE oriented skills do not stack with each other. Meaning that if we send 2 commanders on an attack/resource gathering mission (for example) and both share skills of increased debris, or field size, only the highest will apply. Skills DO stack on PvP oriented skills such as increased damage/armor.