What is the difference between wisdom and hero medals?

Wisdom medals are earned from event rewards and are used to unlock and upgrade hero skills. You will need a lot of these to upgrade the skills.

Hero medals are received when you recruit a hero that you already have, or if you split a hero. You may also get a few from rewards. You also need these to unlock certain hero skills, in some cases you need 1 or more medals of a specific hero to unlock a skill. You can also exchange these in the Arena building for wisdom medals.