The Berserker is an Trooper that is unique to the Wookiees, and is available at the Fortress in Tech Level 3. It is an effective hand-to-hand fighter, better than the Mounted Trooper for taking down Mechs and Heavy Weapons.
In Tech Level 4, it can be upgraded to the Adv Berserker, which has more hit points, attack, armor, and pierce armor.
"Unique to the Wookiees, Berserkers are highly trained, ferocious warriors that can quickly close the distance with any foe. They're superior to Mounted Troopers in their ability to rip apart enemy Mechs and Heavy Weapons platforms. They also benefit from Self Regeneration, an upgrade in the Command Centre."