So while I was bored I surged the Web and found this:
http://www.dandwiki.com/wiki/Death_Knight_%283.5e_Class%29
Which appears to be some sort of Death Knight homebrew class for D&D. Forget the class and skills (which have lovely descriptions), and look at what he wrote on the Code of the Death Knight.
Death Knight Code:
Lawful Evil
The First Allegiance is to Death, not Life. The first allegiance demands that the Deathknight show no mercy in combat. He strikes to kill, always. The first allegiance also demands that the Deathknight take no special care to stave off the death of others. A fallen comrade is considered weak, thus useless to the group and party. Incidentally, these, together, make it very hard to take prisoners. Deathknights often will make a point of murdering those who they've "only" incapacitated, though this is not always a rule.
The Second Allegiance is to Undeath, and its Glory. The second allegiance demands that a deathknight further the cause of undeath. If the undead are rampaging, he takes command. Deathknights do not oppose the undead without due reason (i.e. the undead being itself is opposing death and undeath, or harming the cause of death and undeath).
The Third Allegiance is to Honor, as it lasts for all of Eternity. The third allegiance demands that a deathknight be honorable. In this, his word is his bond, once sworn he shall uphold it so long as his trust is not broken, even against his convenience. After all, the undead live forever. An additional ramification is that many deathknights contract themselves to limited durations, aware of the possibility of rising as undead themselves and being still sworn to their bond. Deathknights also are very keen to exact vengeance for slights against them, or return favors for previous kindnesses. Honor demands it.
Lawful Neutral
The First Allegiance is to Death, not Life. The Death Knight forsakes everything that binds him to Life, his desires, his feelings, his loved ones. He exists only to serve death. He must protect sites where the dead are laid to rest, and he must ensure that all slain allies and enemies receive proper rites for their passage to the afterlife. Only death itself decides when to take a life, and it is not for mortals to question this decision. Magic that brings the dead back to life is forbidden, and the Death Knight may neither use it himself nor accept the use of it for himself. Only direct divine intervention can bring a Death Knight back to life (Wish or Miracle spell). Only divine mandate should dictate if the Death Knight should live past his/her due time.
The Second Allegiance is to Death, not Undeath. The Undead try to cheat the natural cycle of life, and the Death Knight must use every available means to stop them and restore natural order.
The Third Allegiance is to Honor for all of Eternity. The third allegiance demands that a Death Knight be honorable. In this, his word is his bond, once sworn he shall uphold it so long as his trust is not broken. His word is to stand forever, like death itself. Death Knights are expected to repay kindness with kindness and insult with vengeance.
Ex-Death Knights: If you break an oath, agreement or contract, or grossly violate the Death Knights code you lose your class abilities, and you may not progress any farther in levels as a Death Knight until an Atonement spell is cast on you.
Although there are no Death Knights in the mud, Dk do not have anything to do with Undeath, and that most DK's tend to be chaotic, as were the Legion DK's.
But for me the stapple of DK is a Lawful character. A Knight, that is evil but still has some honor.
Like evil kings and emperors, who use rule of law with an iron fist.
The classic example being Dart Vadder, and the Emperor.
PS: Just look at this skill description:
Death Armor: The air grows colder. Your armor starts to give off a faint black light and the earth where you stand becomes barren of life; The death armor has come.
