Black Knights are an intimidating presence in any fight, towering over foes with their huge armor and terrifying reputation. Epitomizing the principles of physical defense and protecting allies first learned as Soldiers, these warriors use the power of the Black Wind to force enemies to fight on their terms.
They can cleanse negative statuses that would affect their battle performance, such as Fear, Hesitation, Charm, Poison, negate On-Hits from the enemy and even Rampaging. All of those with nothing but strength of heart and willpower! (And Momentum.)
They have AoE and two gap-closers, which are good to save momentum if the enemy is close or just adjacent to your position.
High emphasis on reducing physical damage. Black Knight paired with Demon Hunter's Matador Stance often has good results. (Destiny: Soldier just makes it better!)
Stalemate will make sure Swords, Axes and Spears will tickle you. As long as you have the DEF required to increase the chances, of course.
Tons of free Critical Evade! Needless to say, they're the natural counters to critical hit-relying classes, such as Duelists and Void Assassins.