Okay so a bit of worldbuilding for The Fierce Forests' world! (Under the readmore!)
The magic system is kinda a weird thing. Magical elves and necromancers are born with magic, but humans have to "earn" their magic via classes. Knights and guardsmen that serve their nobles are usually given these classes to learn how to use magic. If they pass, their teachers "pass" down the magic for them to use from then on.
Nobles like King Brennus, however, can get access to magic without classes by buying their way with thousands of gold (haha IRL). Some nobles opted for just basic spells like Fire and Ice. Others, however, like Brennus, go for the strongest spells like Inferno (most powerful form of Fire) and Snowstorm (most powerful form of Ice). They must be careful, however. Getting the strongest spells can fry one's brain.
Brennus' filter when he was younger was gone due to his brain being fried from getting too much of the powerful spells, therefore making him a fearsome tyrant to this day. There are other factors as to why he became that way, of course, but too much magic made it worse.
(If anyone has any ideas, comments, or any logistics, let me know!)