Rise of Civilization has an elaborate system of commanders, that can benefit your game play in various way. This guide explains the commander system.
There are 34 Commanders in Rise of Kingdoms that can help you with the various activities in the game. A lot is focused on player vs player (PvP) combat, but they can also help with battling barbarian (PvE) and gathering resources.
Each commander has a grade: Advanced (Green), Elite (Blue), Epic (Purple) or Legendary (Orange). In general the higher the grade the better the commander, but the higher grades are also more difficult to improve and the Legendary commanders cannot be acquired without paying.
Each commander has a certain civilization it is associated with. When you chose your civilization at the start of the game, this will determine which commander you start with (the Epic commander of that civilization, note that you can change your civilization later on, but this will not affect your starting commander). As far as I have found out this is the only effect of your chosen civilization on your commanders, e.g. it does not affect the chance of getting other commanders.
Each commander has 4 (Advanced and Elite) or 5 (Epic and Legendary) Skills. These skills are the basic identity of your Commander (although quite some commander skills are similar to other commander skills). Typically the first one is an Active skill that will be activated once the rage meter reaches 1000, accompanied by Passive skills that do not need to be activated. Initially only the first Skill is unlocked. Unlocking the other Skills and improving the skills will make your commander more effective.
Each commander has three specializations, which correspond to three talent trees that are available to assign points you will acquire as you level up your commander. These talent trees are a great way to improve the effectiveness of your commander and the troops he is leading.
Basically whenever you send out any march for any activity you can add one or two commanders to the march to help you with any activity your troops undertake, whether that is battle, gathering, or you just want to improve the speed of your troops or the amount of troops in a march. In addition you can also set commanders to help with the defense of your city.
You can always use one commander, but you can only use a secondary support commander if the first selected commander has been upgraded to three stars. It might not be smart to right away upgrade a commander to three stars, so first read the section on improving your commander before going ahead.
To maximize the effectiveness of your commander and troops you should always make sure they complement eachother, e.g. a commander focused on cavalry should have (mainly/only) cavalry troops in its march, a commander that provides a wood gathering boost should be send with troops that are gathering wood.
When you click on your Wall and select the shield menu, there are two slots at the left top that allow you to specify a primary and secondary defense commander. For attacking there is a strong argument to be made for using commanders that complement one specific troop type, but since in your city you normally have a mix of troop types, you can better chose to have commanders that benefit all troop types.
Opening Chests in the Tavern is the way to get new free Commanders, the Legendary ones you need to purchase with real money. The rewards are random, you won't always get a commander and it will take some time before you have all free commanders. Getting the commanders you want is only the first step, selecting the commanders you are going to use and improving those is the more time consuming task.
You can get one silver and one golden key by completing the Daily Objectives.
There are two ways to improve your commanders. One is to increase your commander's XP level, which can be done by assigning Tome of Knowledge items in the commander detail screen. When you increase the XP level you get talent points which you can use to assign in one of the talent trees that are available for the commander.
A bit more complicated are the skills. You need to upgrade the Star level of your commander to unlock new skills. To be able to upgrade to a next star you need to upgrade the XP level, 2 Stars require XP level 10, 3 Stars XP 20, 4 Stars XP 30, 5 Stars XP 40. Once you have reached the required XP level the upgrade (arrow up) button next to the stars becomes active. When you click this you should assign Starlight Sculptures to upgrade to a next Star. Each commander grade has its own Starlight Sculpture (Dazzling for legendary commanders, Brand-new for epic commanders, Ordinary for elite commanders, Obsolete for advanced commanders). You can manually add the Sculptures or Auto-Add them, and use the Develop button to confirm and upgrade. Besides unlocking the Skills you can also upgrade them. This can be done by using commander specific sculptures. These sculptures can also be acquired via the chests in the Tavern, and can be purchased in the Medal Store in the Expedition. There are also for each grade generic commander sculptures that you can use instead of the commander specific structures. When you have assigned enough of the sculptures (via the Skills button in the commander screen) you can use the Upgrade button.
With upgrading Skills it is important to realize that you cannot select a SKill to upgrade. One of the unlocked (and not yet maxed) Skills will be selected at random. For commanders it can be desirable to upgrade the first Skill to the maximum before you unlock more Stars.
One of the most difficult choices in the game is which commanders to focus on. Improving a commander (upgrading XP level, unlocking Skill, Upgrading Skills) is requiring a lot and you need to focus on which commanders you plan to use so that you will have a selected set of strong commanders rather than a very large set of commanders that are just average. If you are a big spender you can just select whichever commanders best suit your game play, but if not, you have to realize that just purchasing a Legendary Commander might seem nice, but it is only the beginning and improving a Legendary commander is also more difficult than improving the lower grade ones, because the required items are more difficult to get and/or you need a lot more of the required items.
Besides the amount of money you intend to spend, it is also important to determine which commanders best complement your game play. It is always good to focus on commanders that can improve your gathering rate for all marches you send out to gather. For PvE combat, you might consider whether it is really worth it to focus on commanders that help you, or whether it is better to focus your efforts on PvP commanders. If you are one of the stronger players in your alliance, you might want to also pay attention to commanders that have rally improvement, and increasing your march capacity is more important. Another choice is whether for attack you prefer to focus more on commanders that complement one specific troop type (if so, which) or a mix of all troop types. If you train all different troops at least having two commanders that strengthen a mix of different troop types is useful to set as the commanders to defend your wall. If you go for single troop type for attack you might consider cavalry, a large benefit is its high basis speed which can be improved further with commanders. Being able to attack fast, or escape when faced with stronger opposition, is very valuable.
You guessed it already, if you are looking for which commanders to use, this is not the right place. I am more sharing considerations and in the next paragraph will discuss what data and tools are available on this website to help you make your choice.
The links below take you to various parts of this website that can help you with selecting which commanders to focus on and how to improve them. The commander overview not only shows all available commanders, but also provides lists of commanders for each civilization and each talent specialization. For each commander you can see the details of the commander including the available skills.
There is also an overview of all talent trees, which for each tree the commanders that have this specialization and the details of all projects in the tree, including a cumulative overview of all boosts the tree can provide.
In the commander talent tree planner you can try out different configurations of the talent trees for each commander. Best to register if you are interested to use this tool, so that you can save the different configurations.
This guide should give you a good understanding of the importance of the commanders and how it works, including the sections on this website that can assist you in your gameplay.
Tool(s): Talent Tree Planner