His skill is charging at the highest HP enemy dealing AOE DMG, also taunting and stunning the target for a period of time. This attack also causes the target to take more damage from attacks and decreases the amount of HP they can recover from other skills. It is a high cooldown skill (17 sec after skill used) but reaches 1 rage cost (at lvl 18).
Berserker functions primarily as both a tank due to his very high HP and an anti-tank due to his specialised skill. Because of this a Dragon Heart is probably the wisest choice of equipment for him, boosting his HP, DMG reduction and his chance of HP recovery.