
Crest of the paladin.
A paladin is an individual with a mastery in the melee combat of a warrior and the power of the Holy Light of a priest. Paladins are considered "warriors of the Holy Light", combating for all that is good and against those that are evil, such as the undead, and the Burning Legion. The call of the paladin is to protect the weak, to bring justice to the unjust, and to vanquish evil from the darkest corners of the world. These holy warriors are equipped with plate armor so they can confront the toughest of foes, and the blessing of the Light allows them to heal wounds and, in some cases, even restore life to the dead. Ready to serve, paladins can defend their allies with sword and shield, or they can wield massive two-handed weapons against their enemies. The Light grants paladins additional power against the undead and demons, ensuring that these profane beings corrupt the world no longer. Paladins are not only zealots but also guardians of the righteous, and they bestow blessings on those the Light would shine upon. The Light radiates from paladins, and worthy allies who stand near them are emboldened by its power.
History

Paladins and death knights fighting at Lordaeron.
The first paladins may have been draenei, who were introduced to the Light by the naaru after fleeing their home planet of Argus. Zandalari troll prelates are paladins who worship the loa Rezan.
After the Orcish Horde sacked the city of Stormwind, a mass exodus took place to the north to seek help. The Archbishop Alonsus Faol had perceived that the pious Clerics of Northshire, who had suffered such terrible attrition in the First War, were ill-suited for the dangers of combat. Along with many of the surviving clerics, he sought those of only the greatest virtue among the knighthood of Lordaeron and tutored them in the ways of magic. The first generation of paladins had spawned the Order of the Silver Hand under the leadership of Uther the Lightbringer during the Second War as a way to counter the orcish death knights. Paladins were also quite useful in combating the undead, as paladins were immune to the plague. Paladins were also known to minister to the masses during the war, gathering inside churches to deepen their faith. Through meditating, communing and tithing at these sanctified sites, they discovered new ways to channel their healing and spiritual powers.

Prince Arthas reflecting over his choice.
Although the paladins were once loved and revered throughout the lands of Lordaeron, by the time of the Third War, they had since fallen into hard times. Pressure began to surmount with the creeping plague of undeath creeping up the countryside. The entire Order of the Silver Hand was disbanded by Arthas Menethil for refusing to kill innocent townsfolk of Stratholme who were believed to be contaminated by the dreaded undead plague. Disenfranchised and driven from their former homes, the paladins still worked selflessly to protect humanity from the gnawing jaws of evil. Many paladins traveled to quarantined lands to ease the suffering of those left within the plague-ridden colonies, but although the paladins were immune to disease of any kind, they were persecuted by the general populace who believed that they had been infected by the foul plague. Some of these paladins traveled to Northrend. When they finally reached the icy fortress of Ner'zhul, embittered by the trials they had to suffer through, they had become dark and brooding. The Lich King offered them untold power in exchange for their services and loyalty, and they accepted to become death knights to his service.
The humans of Stormwind and the dwarves of Ironforge train their own paladins and consider themselves Knights of the Silver Hand. The human paladins spread their order to the dwarves of Ironforge. The paladins who remained in Lordaeron continued to fight against the Scourge. The Scarlet Crusade evolved from the Knights of the Silver Hand dedicated to the eradication of the undead from Lordaeron, the Forsaken and Scourge. However, the Crusade grew corrupt from within by paranoia, mistrust, and manipulation from the dreadlord Balnazzar. Many saw the zealous and fanatic Crusade had fallen from their once-noble purpose and left to form their own order: the Argent Dawn.
The Hand of Argus is a order of draenei paladins and vindicators based in the Azuremyst Isle. The blood knights are a order of blood elf paladins formed by sapping Light energy from the captive naaru M'uru, desperate for sustenance after long years of enduring the collapse of the Sunwell. However, once the Sunwell was restored after Kil'jaedan was banished, they channeled their power directly from the Sunwell.
Tirion Fordring restored the original order of the Silver Hand in Lordaeron, which later merges with the Argent Dawn to form the Argent Crusade.
The Sunwalkers are an order of tauren paladin, who recently learned to use the power of the sun - much as druids use the power of the moon - to wield the Light and become paladins.
During the third invasion of the Burning Legion and after the defeat of the Argent Crusade in the Battle for the Broken Shore, the Silver Hand was formally reestablished and supported by each major paladin order on Azeroth. Tyr's Guard is a secret order sworn to protect the tomb in Tyr's Fall who learned how to wield the Holy Light, and they became mighty paladins.
Lightforged draenei of the Army of the Light ended up joining the Alliance during the Argus Campaign and after the defeat of the Burning Legion.
Code of Conduct
As "warriors of the Holy Light", paladins uphold all that is good and true in the world and revile all that is evil and sinister — especially undead and the Burning Legion. They offer assistance to the beleaguered and smite their enemies with holy fervor. Found in almost every corner of Azeroth fighting the forces of evil and barbarism, these stalwart, zealous warriors ceaselessly maintain their vigil. Paladins are the embodiment of good and selfless dedication to the protection of their peoples. Their passion and fearsome resolve can lead them astray, however. Most notably, the Scarlet Crusade, a faction of paladins and priests who broke away from the the Knights of the Silver Hand, took their commitment to eradicating the Scourge so far that they turned on their former allies, suspecting anyone whom they believed carried the "taint" of the undeath.
Paladins don't always have to work within good or neutral organizations, as seen by the Scarlet Crusade and others — however, they do have to believe they are working for good organizations or have faith that their cause is good and just. A paladin can be evil - as illustrated by Renault Mograine and Arthas before he took up Frostmourne - , but as long as they believe their cause to be just, the Light will continue to serve them because wielding the Light is a matter of willpower and faith in one's own ability to do it. Since he felt conflicted, Arthas's ability to use the Light began to wane after he culled Stratholme. He perceived this as the Light choosing to abandon him, which weakened his faith in it further.
Similarly, the Light cannot be forcibly stripped from a paladin that personally conducts himself in an honorable manner. When Tirion Fordring defended the orc Eitrigg from his fellow humans, he was banished from the Order of the Silver Hand, and a ceremony was performed by Uther the Lightbringer to strip him of his power. However, the ceremony failed, and while Tirion accepted his sentence of exile, he retained his paladin powers.
Notable Paladins
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