A barbarian is a strong fighter that rely on his physical prowess and that channel his rage to accomplish astounding feats
The clichè is for a barbarian to be a powerful killing, nearly unstoppable while in its rage, they also can easily ignore enemy's magic. the downside is after the rage when he remain fatigued for some turns
Barbarians are faster than normal humans (speed 4), can whitstand a large amount of damage (they are generally tall and musculars) ignoring pain (especially when in rage). They are heavy hitter especially in rage and can deal awesome amounts of damage.
This is a image i had made some time ago. I reshaded it a bit and edited some parts:
About stats i would make those:
Spell resistance 50%
Rage effect: Attack +10, hp +40, maxhp +40, armor +3, pierce +3, speed +2, +1 action, spell resistance +50%, trample. Duration 4 turns.
When the rage effect wear off you loose all those bonus (you also loose the 40 hp you gained, like receiving 40 damage, so, if you already had less than 41 hp the unit dies) and gain those penalties: -10 attack, -3 armor, -3 pierce, -2 speed, -50% spell resistance. Duration 3 turns (i didn't make 4 because the first turn of the rage you have used up your action to enter rage)