In the world of fantasy role-playing games, a young person is sometimes called by his or her deity to a hard life of service.  The character pledges unquestioning faith, unwavering courage, and constant charity.  Thus a paladin emerges. 

The basics

A paladin is modeled on the classical Arthurian knight — chivalrous, devoted, and brave.  The paladin can be one of the more difficult characters to effectively role play and perhaps the most difficult to qualify for.  In some game systems, paladins have to be human, and in others, species/race does not matter.  Elf and dwarf paladins are common, although, in the Dungeons & Dragons system, I've always wanted to play a halfling or gnome paladin, if only for comic relief.  Several qualities make up a good paladin. They must possess a high charisma, as they must always admirable and respectable.  Being essentially fighters with a divine calling, physical strength is essential.  A paladin also needs to have wisdom or intuition since they have the potential to cast clerical, or divine, spells. More than anything else, however, a paladin must rigidly and unfailingly follow a strict moral code.  Thus the paladin is required to be aligned lawful good.  Some dungeon masters require that the paladin follow a specific deity, take vows of poverty, limit the amount of magical items they may use, or require the paladin to tithe.

Role-playing the paladin

This moral code can either be quite entertaining or quite annoying, in role-playing terms, depending on how one does it.  For instance, often a less-experienced gamer will play a paladin as if she were a naïve Judeo-Christian prude.  This sort of character moralizes and proselytizes endlessly, forbidding rogues from thieving or assassinating and fighters from executing the orc chieftain the party just captured and questioned.  I have seen more than one game session derailed because we needed to take a surviving bad guy to town to be properly adjudicated by the legitimate authorities.  On the other hand, I have seen characters play their paladins as crusaders, knights errant, champions of retribution and vengeance, and religious fanatics.  These characters all satisfy the requirement for following a strict moral code — not necessarily one most people in the real world would agree with — but are much more fun to be around in game terms.  In any case, no paladin can knowingly or willingly associate with evil characters or characters that continually and flagrantly defy his moral code.

However one chooses to play the paladin, the character's behavior must strictly conform to the strictures the dungeon master and player have agreed to.  If the character behaves cowardly, unjustly, or in anyway against the code, the DM has the ability to rob the character of his powers.  This represents the deity withdrawing her favor from the wayward warrior.  In game terms, this means the character is nothing more than a fighter.  To get these back, the paladin must atone for his transgressions in some meaningful way.  If the paladin willingly commits an evil act, the DM will probably decide that he may never become a paladin again.  In any case, it is always a life changing event for a paladin to be stripped of her powers. The change might be so traumatic that the character chooses the way of the blackguard, or anti-paladin — the quintessential black knight.  That's when the game gets really interesting.

The powers

The powers bestowed upon the paladin by virtue of her divine favor are quite impressive and more than make up for the limitations of the chivalrous lifestyle.  They vary from game system to game system, but here are some common ones.

  • Foremost, the paladin has the ability to heal by laying her hands on himself or others. 
  • The paladin also enjoys incredible health, being impervious to all diseases.  This divine grace also translates into better luck in avoiding misfortune, or in game terms, bonuses to saving throws.  
  • Paladins have the innate ability to Detect Evil
  • More experienced paladins gain immunity to fear effects and help bolster the courage of allies nearby.
  • These paladins also gain the ability to cure diseases in others and repel or destroy the undead as if they were clerics. 
  • They can also smite evil by channeling their righteous fury into a single blow against a maleficent foe. 
  • Some paladins can cast clerical spells and may summon supernaturally enhanced mount.

Incidentally, the word "paladin" is an old one. Various etymology sites I've visited agreed that the term has long been associated with the 12 Peers of Charlemagne, his most trusted and noble knights. This usage derives from Middle French paladin, meaning "a warrior." Following this to the Latin, there is palatinus meaning "palace official." I have also heard that the word has Arabic origins dating back to The Crusades.

Sources:
dictionary.com
WWWWebster
http://www.geocities.com/etymonline/p1etym.htm
and others