Given the size of this guide in comparision to the last, I will say that undead, especially Death knights, can be prone to amnesia. You may create one first and digest the guide for a character backstory later if you wish, but at the very least you should take into account what being an undead entails. This is touched upon in The Death knight section
The Worgen Death knight origins
1) Pyrewood resident
Worgen Death knights have a given backstory that can be summed up by this text in the quest in which you execute an Argent Dawn member you once knew.
Lord Harford says: Come to finish the job, have you?
Lord Harford says: You'll look me in the eyes when...
Lord Harford says: <Name>?
Lord Harford says: <Name>, I'd recognize that face anywhere... What... What have they done to you, <name>?
Lord Harford says says: You don't remember me? We were both servants of Arugal back in Silverpine Forest. We put up with his merciless torture for ages. It was you who saved me on that fateful night when we escaped Shadowfang Keep.
Lord Harford says: Without you I would have died. YOU! The most noble worgen I ever knew.
Lord Harford says: What have they done to you, <name>? How could this have happened?
Lord Harford says: Remember the worgen you once were, <brother/sister>! You were our savior! Fight this!
Lord Harford says: Listen to me <name>. You must fight against the Lich King's control. He is a monster that wants to see this world - our world - in ruin.
Lord Harford says: Don't let him use you to accomplish his goals. You were once a hero and you can be again.
Lord Harford says: Fight, damn you! Fight his control!
Knight Commander Plaguefist yells: What's going on in there? What's taking so long, <name>?
Lord Harford says: There... There's no more time for me. I'm done for. Finish me off, <name>. Do it or they'll kill us both. <Name>... Remember Gilneas, our beloved home. This world is worth saving.
Lord Harford says: Do it, <name>! Put me out of my misery!
Now you might be wondering how your character can be a Gilnean and a somewhat-cured worgen that existed before the Cataclysm. Wasn't this impossible until Krennan had made a chemical 'cure'?
When the Greymane Wall was built in the years following the Second war, it was actually built in a way that cut off a part of Gilneas called Pyrewood to allow for a secure natural barrier around the wall. This was what enraged Darius Crowley, a noble of the land, into starting the Northgate Rebellion - an act that saw him jailed in Gilneas sometime after the Third War. A lot of Gilneans in Pyrewood remained there, outside of the Greymane wall, for whatever reason.
When the Third War came and the Scourge were attacking the Greymane wall, destroying the Gilnean soldiers sent down to fend them off, Genn Greymane had the necromancer Arugal summon the worgen to tear down upon the Scourge. This worked - but the worgen, being worgen, killed the humans as well. The traumatised mage Arugal went mad and somehow adopted the worgen as his own - likely bringing them under control with his enchanting-supported magic. He retreated to Shadowfang Keep with the worgen, falling under the command of a sentient one titled Alpha Prime. The worgen that was once a Kaldorei encouraged him to spread the worgen curse to Silverpine and elsewhere.
Arugal used the Council of Pyrewood to keep the villagers under his control whilst he tended to other matters, casting enchanted shackles upon the populace of Pyrewood. This cursed them in a way that would force them to turn into feral savages by night - but by day their free will and human forms remained, unless Arugal deemed them a more favoured servant, in which case they could be granted more free will and retained intelligence with their curse. Arugal's experimentation with the curse could explain how they change between human and worgen forms - Lord Harford shows up lucid and in worgenform before you kill him after all, his lucidity in the form granted by Arugal, though for Death knights it may just be that undeath dealing with the feral aspect of the mind grants the ability to shift forms, just like the Ritual of Tal'doren.
Pyrewood's Death knights escaped the enslaved town, died, and had their corpse taken by the Scourge to join the rest of the bodies mass-raised for potential Death knight candidates.
This means that, realistically, there would be very few worgen Death knights with this background. Pyrewood wasn't exactly a large settlement. It is also possible to imagine worgen that escaped Shadowfang Keep and/or Pyrewood's dictatorship not becoming Death knights - Lord Harford was one of them, a noble of Pyrewood.
2) Other human
You may not necessarily have to be Gilnean - perhaps a weary adventurer or two came across Pyrewood in their time and fell into enslavement, having no other options for survival in a Scourge-wracked land.
Whilst Arugal, employed by the Scourge no less, was present in Northrend infecting humans with the worgen curse, it is uncertain when exactly he was ressurected as a shade and dragged off to aid the Scourge with his arcane knowledge. As cursing and enslaving a town takes time, it could of taken place before the battle at Light's Hope Chapel, in which case perhaps your Death knight was sent there with the undead giants and whatnot.
On the plus side, the Grizzly Hills Wolfcultists/slaves appear capable of free will and shapeshifting too. So if one is unsure of undeath granting that capability, it helps.
There are also still Death knights being made in the Plaguelands via a ritual. Though the Forsaken breaking free when Arthas' control was weakened could apply to the Lich King's death too and items like the sovereign rod exist to free undeads, they are not fullproof and anything outside of the Light's Hope Chapel event could be seen as quite a shaky foundation for a Death knight character.
During the Third war, Arugal summoned the worgen in an attempt to combat the Scourge assaulting the Gilnean wall. Unfortunately, what he summoned were Kaldorei druids dating back to the War of the Ancients that could not handle the sheer ferocity of the worgen form and were 'put to sleep', so to speak. They turned on the human soldiers as well and the rest is history. It is not difficult to imagine the Scourge slaying one or coming across a dead one to drag to Acherus.
There are two major problems with this - Kaldorei are generally trickier to Rp, especially as Death knights, and the game mechanic shifting abilities will shoot immersion in the foot if you ever pop out of worgen form. Even if you play them as one that will not or can not shift, either from your interpretation of undeath's effects on the curse or the character forgetting how, the fact your non-worgen form can never apply to your character may be enough to put some off.
If you are serious about rolling one, I would recommend reading A Guide to Roleplaying a Night Elf character, it even has a section on Death knights. If they were one of the sleeping druids, such a character would be over 10,000 years old and most likely male - it would take some time before female druids and male priests were allowed. Or perhaps a Kaldorei adventurer went to Silverpine within the last five years, was bitten and died.
4) High elves
It is possible to imagine a High elf that passed by or came to stay in one of the above mentioned human communities, or one that sired a half elf there. However, High elves tend to snub humans, and after the Third War about a decade ago, the snubbing would generally worsen. They would need a real reason to stay in a place where they would be the odd one out.
You would need to decide roughly when your character died and why they did not join the Sin'dorei, as a human/worgen model is far more convincing than a Blood elf one that cannot shapeshift. Knowing the political differences between Quel'dorei and Sin'dorei is important, as 90% of the survivors formed the Blood elves. If your character died early enough to wake up one day to suddenly find a huge division within their race, what shall prompt them to rejoin the smaller one - or just the Alliance in general?
I would honestly just recommend the first example. The other three are more to cover the possibilities than anything and may come off as a bit too special-snowflakey. Even as recently as a few months ago people were outright saying the given worgen Death knight backstory was lorebreaking, so having to constantly back yourself up on anything else would likely get frustrating.
The Death knight
I would recommend reading this guide if you want a very in-depth look at Death knights. For the sake of this guide, I will try and give some brief but vital pointers that are a must-have for any Death knight character.
- You are undead. No exceptions. No, you cannot get past this with the worgen curse being a potent nature-related form, Arugal experimentation or being a second generation Death knight(Which hasn't been seen with the worgen curse) seeing as they would of all turned dead by now anyway.
- The holy Light can heal you, but it hurts. A lot. Because you're undead. Being healed by your death coil spell or a Shadow priest is a lot more comfortable for a Death knight. Nature magic would do nothing for them.
- You are not perfectly intact to the point of looking on par with the living. The emotional state of the risen candidates that are deemed unworthy and eaten by ghouls is blamed on them not being dead long enough by Instructor Razuvious. Signs of looking dead set in quickly after death, and taking a corpse to a floating citadel takes time.
- You do not have a sex drive. The Scourge are not going to bother instilling a distraction into their killing machines and sex drive is quite dependant on the state of your reproductive organs. Even if a necromancer tried to empower a corpse with this ability, a worgen is an unlikely candidate given that they are tricky to raise into undeath, and even Forsaken candidates for Death knights are killed and risen again anyway. Which brings me to...
- Your emotions are stunted, to a degree. This doesn't mean that your Death knight cannot have any emotions at all (Hell, Koltira and Thassarian were enemies by faction in life and got along well in undeath) - literally no emotions would be dull to play. But any risen Death knight candidates that showed too much emotion were just fed to the ghouls. Think practical, negative emotions with less positive ones now that your character is undead.
- You better be good at combat. It may seem comical or original to envision a weak Death knight character, but this is actually more sueish than the overpowered ones because at least it makes sense for an overpowered individual to of come out of the starting zone in (largely)one piece. Try and make your character one that was skilled with melee combat in life.
- You have to cause agony or risk falling into a mindless bloodlust. It isn't clear how often, but this rules out a torture/killing-free unlife on a nice holiday resort.
- Don't show your mindless ghoul to just about anyone! Performing necromancy is still illegal, regardless of the fact that you are legally welcomed into the Alliance. Save it for when no one is looking - or when no one that takes issue with it is looking.
- You need your runeblade to use your Death knight-related spells. Game mechanics imply some could be cast without a runeblade, but this is perhaps just game mechanics. It is also possible to see a Death knight taking up alternative forms of magic in case they should drop their blade in a fight, but this runs the risk of looking overpowered and having to explain every time why your Death knight just cast a fireball.
- You are welcomed, but not strictly wanted. By Varian's law, your character has rights on par with any ally of the Alliance. This won't make others forget the atrocities of the Scourge however, regardless of whether it was your fault or not. Undead have been a problem longer than they have been useful to the living, and your average citizen wouldn't of had enough exposure to helpful ones to change their minds. It is not difficult to imagine the people avoiding them in the streets, employers blatantly not hiring them out of discrimination, or Kaldorei trying to destroy them when the human authorities' backs are turned...
Are Worgen Death knights Lorelol?
Strictly speaking, no - they have been implemented into the game with at least one character validating their presence. The confusion regarding their validity comes about because the Val'kyr were unable to raise worgen-cursed bodies in Silverpine as Forsaken. This was answered in Ask CDev 2 as to why the Val'kyr couldn't raise them - they just aren't as powerful as the Lich King (And perhaps the human necromancers involved in raising Death knights) and the worgen's ties to nature makes them harder to raise.
Adding to the confusion is the fact that they weren't seen prior to Cataclysm's release - their existance was pretty much retconned in later. The playable races wouldn't of been the only candidates for being risen as the Scourge as Death knights, however - Vrykul ones are in game, and trolls besides the Darkspear are pretty widespread.
There is also the matter of them having free will once they break free of the Scourge instead of being a mindless feral without inbibing the waters of Tal'doren, however this could of been explained away by Arugal's experimentation. In Ask CDev 3, it was finally explained as the mind control over Death knights snuffing out the feral aspect to leave the human mind in control.
They are shoe-horned in, they are barely explained and raise questions with little information to answer them with as to their state - but they are not lorebreaking.