Primary skill
 Attack |
 Defense |
 Power |
 Knowledge |
| Primary skill symbols which recur almost in the same form throughout the game. | |
Primary skills are characteristics of heroes and creatures. There are four different primary skills: attack, defense, spell power and knowledge. Each time a hero reaches a new level, one of their primary skills is advanced by one point. Attack and defense can be categorized as might skills while power and knowledge are magic skills. Might heroes, like Knights and Rangers, advance more rapidly in might skills as for magic heroes, like Wizards and Warlocks, advance faster in magic skills. The advancement in primary skills vary considerably by the hero class on levels 1 to 9, but after that, hero's advancement generally becomes more balanced.
Attack skill together with defense are the main factors affecting the amount of damage creatures deal under the hero's command. A hero's attack skill value is added to each of the stack's attack rating, increasing the amount of damage they can inflict in combat.
For each extra point of Attack skill over defender's Defense skill, the inflicted damage gets increased by 5 % (up to 300 %, which is 60 points in difference).
Defense skill works in similar way to attack skill. Heroes' defense skill is added to the defense rating of each of the creatures in their army, which decreases the amount of damage they take from enemy attacks.
For each extra point of Defense skill over attackers's Attack skill, the received damage gets reduced by 2.5 % (up to 70 %, which is 28 points in difference).
Power skill (or sometimes spell power) is the main factor for duration of many essential spells like Bless, Curse, Haste, Slow and many others (1 point of Power skill equals 1 round of duration), the amount of health points taken by damage spells and restored by beneficial spells, and efficiency of miscellaneous spells (e.g. ones summoning elementals). Efficiency of some spells, for example of the majority of those cast on the adventure map, doesn't depend on Power skill.
Knowledge skill determines the maximum amount of spell points a hero may have. It is calculated by multiplying knowledge with 10, so knowledge of 13 would give a hero a natural maximum of 130 spell points. With the Intelligence secondary skill, this natural maximum can be increased up to double (in HotA 
it has been nerfed to only increase the mana pool by 50%). Additionally, visiting a mana vortex or a magic spring hero can temporarily double the spell points, which means that with expert intelligence, the maximum spell points will be quadrupled (tripled ) from original amount.
By default, all heroes have at least one point in power and knowledge skills. However, a map-maker can set these skills to 0. In that case, the hero will look and function as if the value would be one. When the hero receives the first point to the skill, they will still have only one point in it, but after that the points accumulate normally.
