Heroes are the biggest part of your force. You will need to train them and keep them equipped with troops. Heroes come from Campaigns and Prestige. It is important to note that there are four types of Heroes: Siege, Gambit, Spell and Support.
You have 5 starting heroes to choose from. All starting heros have a gambit attack except Rickon. The heroes are:
Fernando : Unit: Cavalier - No unit bonus, Gambit: Charge. Deal Normal and Gambit Damage
Arya : Unit: Archer - No unit bonus, Gambit: Rush. Deal Gambit Damage and Stun for 1 Turn
Meera :Unit: Swordsman - High Block Rate, Gambit: Entrench. Deal Gambit Damage and enter defensive mode for 1 turn
Rickon : Unit: Catapults - High Critical Strike rate, Skill: Bombardment. Deal High Normal Damage
Grismund : Unit: Huscarls - Average chance to block, Gambit: Battle Cry. Deal Gambit Damage and lower enemy Morale by 30
All of these heroes will lose value by mid game, so don't worry too much about who you pick. There is one permanent effect depending on who you choose though, which is whose portrait you see when you participate in Plantation and Regional Wars.
Adding and Removing
You can unlock your 3rd Hero by simply training Formations to level 2 in your Academy. But, in order to do this you will need to reach Level 11 which unlocks the Academy, then raising the level of your Academy to 10. The rest you will Unlock through Prestige and leveling up Formations.
If you want to switch Heroes then simply Dismiss one. You can do this by clicking the Dismiss button in the heroes status window. Your Heroes level and attributes will all remain the same should you want to use them again.
Siege heroes (Also referred to as War Machines) use Normal Damage attacks only. They do not have Gambit attacks. They do not gain morale and are therefore excluded from morale boosting support heroes (see Priests Bless ability).
Equipment they rely on: Normal damage weapons such as Swords, Bows, Lances, Maces etc. Armor and Cloaks. Crowns are optional.
Most heroes use Gambit and Normal Attacks. Every time their morale is raised to 100 or more, they unleash their gambit attack on their next turn. Otherwise they attack for normal damage. Morale can be raised by dealing or taking normal damage, or with the use of a support hero.
Equipment they rely on: Mounts for improved gambit damage, Armors and Cloaks. Crowns and Normal damage weapons are optional.
Spell casting heroes deal Spell Damage. They are generally seen as a more late-game unit type, as there are no good early-mid campaign casters and only King Arthur has a useful low prestige caster. Good spell damage items are also generally harder to get, thus making Spell casting heroes a choice for high level players.
Spell attacks cannot be dodged or blocked or reduced in damage aside from researching in the academy, however, they have a varying chance to fail (depending on the hero) regardless of the opponents unit type or formation (Normal attacks can be Blocked and Dodged, Gambit can be Dodged).
Equipment they rely on: Enchanted Items (Staves, Books, Orbs etc). Armors and Cloaks. Crowns are optional.
If you are in the King Arthur Kingdom, be sure to gain 20k prestige and aquire Sir Kay, he is a good caster who gains health back for the amount equal to the damage that he does.
Support heroes do not attack. They have a variety of abilities ranging from healing everybody in the formation, to raising your morale, to lowering enemy morale. Clever use of support heroes can lead to the most effective formations, but on their own they are useless.
Priest - Spell: Bless. Targets a random friendly gambit hero and attempts to fill their morale to 100 (Has a low to moderate fail rate) - The first Priest available is Boudica, from Treacherous Revenge campaign.
Flag Bearer - Spell: Morale Boost. Boosts all friendly gambit heroes by 34 morale and reduces all hostile gambit heroes by 5 morale. 100% Success rate. The first Flag Bearers available are William the Conquerer, from Norman Conquest, and Joan of Arc, from Hundred Years War.
Healer - Spell: Heal. Attempts to heal ALL friendly heroes for an amount determined by your spell attack (Research and Staffs boost your Spell Attack value). Has a moderate fail rate (the fail or success is rolled for each hero individually, meaning you may successfully heal 1 hero and fail to heal the others, or you may successfully heal all of your heroes). The only Healer available is Morgan le Fay, from Treacherous Revenge campaign.
Equipment they can make use of: Enchanted Items (Staffs, Orbs, Books etc.). Armors, Cloaks and Crowns.
Increasing Your Heroes Strength
Rebirth is unlocked at Level 51 and can raise the unit level (represented by a Star icon and a number next to their ability in the status window) of your Heroes, when used it will reduce your Heroes Level to 1. Enlightenment is another way to increase stats.