The Black Knight

The Black Knight is an agent of the Lich King, sent to disrupt Tirion Fordring's Argent Tournament.

Icecrown
The Black Knight can be found near the eastern end of the Argent Tournament Grounds in Icecrown. He is involved in the neutral quest chain starting with The Black Knight of Westfall? / The Black Knight of Silverpine? and supposedly ending with The Black Knight's Fall upon reaching the rank of Champion in the Argent Tournament. His mount is named Black Knight's Gryphon but called the Black War Gryphon when riding it.

Trial of the Champion
The Black Knight returned in patch 3.2.0 as the final boss of the 5-man instance the Trial of the Champion within the Crusaders' Coliseum. In the quests The Black Knight's Curse and The Black Knight's Fate, it was revealed that the Cult of the Damned resurrected the Black Knight into undeath.

After flying into the coliseum and slaying a herald of the crusade (either Arelas Brightstar or Jaeren Sunsworn), a fight ensued in which the Black Knight was resurrected once as a skeleton and afterwards as a ghost until he was finally slain by the champions who were training there.

Shadowlands
During the Scourge resurgence, the Black Knight was one of the undead forces reanimated by Mawsworn kyrian at Deathspeaker's Watch in Icecrown.

Trivia

 * His naming, the naming of his relevant achievements, as well as elements of his encounter, are fairly obvious references to the character of the same name from the film .
 * He appears as a legendary card in Hearthstone. His flavor text reads: "He was sent by the Lich King to disrupt the Argent Tournament. We can pretty much mark that a failure."
 * In the TCG, the artwork was used to depict the Unrelenting Rider.
 * In addition, he appears in his skeletal form in the Grand Tournament expansion. The Skeleton Knight's flavor text reads: "Apparently it really was just a flesh wound."
 * The Black Knight has been slain five times. Once in the quest chain at the Argent Tournament, three times during the Trial of the Champion dungeon and once more when he was reanimated by the Mawsworn.