From online games, deriving from "Player Killing". A PKer is one who kills other players for the enjoyment of killing them or causing them grief. See also RPK or RPKer.

The abbreviation "pker" stands for "player killer" and is most commonly used in online games where players fight one another head-to-head, such as Diablo and Runescape.

The 2 letters P and K stand for: Player Kill.
PK'er would be Player Killer.
More than one PK'er would be: PK'ers.

Basically a PK'er is a person who character's sole perpose is to kill other people's characters, for whatever reasons. It can happen in almost in game that let's 2 or more characters go head-to head or duel as some may call it.

Comes from the old style short hand typing inside closed realms of the online game Diablo and/or Diablo 2 LoD.

Symptom:
A PKer is someone who hunts less experianced players on internet videogames. PKer's are considered the murderers in the RPG universe. Usually, a PKer will target someone who is grossly lower in level then they are, if it is an RPG that is. PKers have zero remorse for who they kill, and will eliminate one or more of the same players over and over again. In the popular game, Diablo 2, PKers run rampant in hardcore. There are a few in softcore, but not as many.PKers will get more "pleasure" from killing in HC, due to how once their victim is dead; It stays dead for good. Because of this lovable trait, PKers are rarer in softcore, but still should be looked out for! Pkers will use hacks from time to time to improve their "kill rate". Lagging the game, etc.

Cure:

Usually a PKer is focused on killing weaker people then him, so it's fairly easy to dispose of one with the conventional means.(i.e killing him.)
Pkers will usually, if alone, leave the game if they are outnumbered, or see that they will lose the fight. Pkers who are also skilled fighters are difficult to find- but still exist nonetheless.

Player Killer
An anti-social gamer (...NO WAY!) who takes out the frustration of their Dorito crumb covered, introverted lives on strangers in a video game. That's right, a fucking VIDEO GAME!
The only place people like this can feel some modicum of pride or strength.
That is to say, imaginary and anonymous.

A fan of the Italian Disney sci-fi comic saga "PKNA - Paperinik New Adventures".

One who goes for unexperienced players, players that are lower levels than him, or people that are weaker than him, in both spells and attacks.