You'll have to create a custom unit based on a hero (e.g. Shadow Hunter) and change the model to the berserker model. This allows the unit to obtain Hero abilites and have stats like strength, intelligence, and agility, and also leveling up.
In order to make it "look" like a hero (with the hero glow), you'll need to make a small model editing for the berserker model. But this is just for appearance.