Zeref Dragneel

ZEREF DRAGNEEL

Zeref Dragneel (ゼレフ・ドラグニル Zerefu Doraguniru) is considered to be the strongest, most evil Mage of all time, who possesses extremely dangerous, and powerful Magic. He is the founder and current Emperor of the Alvarez Empire

HOW DID ZEREF "BLACK WIZARD" GET CURSED?

Zeref experimented on forbidden magic which gave him the Contradictory Curse. So the more he values life, the more uncontrollable his power becomes. And when he doesn't value life, the less destructive he gets.

The same curse happened with Mavis who also used the forbidden magic. So basically anyone who experiments or conducts black magic is automatically cursed with the Contradictory Curse.

NOTE: zeref is known as the most dangerous black wizard, and he revived he's brother more than 400 years ago. which is now he has faced he's brother but once he dies, he's brother will not exist along with him.