There have been many paladins in the lands of Azeroth. Some hail from other worlds, such as the Vindicators of the Draenei. Still others are newly come to their powers, such as the Sunwalkers of the Shu'Halo. Ultimately, to be a paladin is to trust in a greater power than yourself to be your sword, shield and balm against the forces that threaten all you hold dear.
Interestingly, the Horde has not one but two unique paladin orders formed in recent years. Of these two, the Blood Knights of the Sin'dorei are interesting not only for the means of their foundation, but also the evolution they have gone through. This evolution is mirrored by that of their Matriarch, Liadrin. A former priest who survived the Scourge onslaught on Quel'thalas and the destruction of the original Sunwell, she lost her faith in the Light and took up the power of a Blood Knight in order to show her spite and derision for the magical force that did nothing to save her city and her people. Yet in time, Liadrin would learn that things were not as they seemed, turning against the Blood Prince Kael'thas himself for the sake of her people.
Liadrin, the first Blood Knight, became in truth as well in power a paladin. All she had to do was suffer the destruction of everything she thought she knew.