The average player will first encounter Edwin VanCleef in Deadmines (at least if they are Alliance, Horde players may miss him all together.) His significance is easily lost as much of the detail of his lore is only touched on with in the game. What WOULD be known is that he is the leader of the Defias Brotherhood , a rag tag band of cut throats who are out to over throw Stromwind. It is his MOTIVATION for this that is frequently lost to players and it why VanCleef feels his cause is just that makes him SUCH an interesting figure.
Sources outside World of Warcraft the Video game will tell you that Edwin VanCleef started out his life the son of a Stonemason who learned every trick of the trade at this father's knee, but in addition to that Edwin had a gift with creating hidden rooms and mechanical devices as well as a childhood friendship with one Mathias Shaw. It was from Shaw that Edwin learned all there was to know about the rogue craft showing a natural aptitude for it. Deciding that a life of crime was more lucrative than a life of hard labor working for his father he used these gifts to become one of the most wanted Criminals in Stromwind. But then came the invasion of the Horde and the destruction of Stormwind.
When the call went out for Stonemasons and artisans after the Second War to help rebuild VanCleef was one of the FIRST to volunteer. He is credited with being the major architect behind the majority of the grander buildings in Stormwind, most notably Stormwind Cathedral.
Now while the rebuilding was taking place King Varian was away helping to round up the last of the Orcs from the Second War and place them in Interment camps. King Llane had been murdered during the war so Varian needed to meet with the other monarchs and strengthen ties, in addition to this he and his young wife had just had their first child, Anduin, named after the recently killed Sir Anduin Lothar another Father figure in Varian's life. (Now I know you are asking, what does Varian lore have to do with VanCleef? Bare with me, it had a BIG impact.)
With Varian off overseeing clean up efforts he left the rebuilding project in the hands of the Nobles of Stormwind. They were to make sure the project was handled in a speedy fashion but most importantly they were to see that the workers got PAID. Unfortunately through means both of the usual greedy kind as well as the more sinister work of a Lady Katrana Prestor while the work DID get done the PAYMENTS never materialized. Apparently while the King was away the Nobles decided to raise the taxes to "pay for the repairs" but then never bothered to pass the money along.
The King and his young family return to find Stormwind on the verge of a Riot. When he attempts to discover WHY the payments never took place and make things right, pandemonium breaks loose and in the confusion his young queen Tiffin is killed. Devastated at this final loss after so many Varian falls into a depression (fed by Lady Prestor) and basically is nothing more than a figure head for the next 10 years.
VanCleef and the REST of the Stonemasons, artisans and workers who the Nobles have cheated are tossed out, accused of killing the queen and disrupting the stability of the nation. With his means of making a legitimate living now removed, as well as being cheated out of what is rightfully his VanCleef swears revenge. Gathering up those others who will follow him he begins to lay a foundation of a completely different kind. The Defias Brotherhood is born.
VanCleef is an interesting character because he gets back to that idea of the "noble thief". He really feels he is "righting a wrong" a "Robin Hood" if you will. And it is really for this reason that I think he was chosen as the Alliance Rogue Armor set. The fact that his organization is all about "Over throwing the government" has lead a lot of people to really question this choice. But really he is all about "vengeance to settle the score" at least in his mind and in Lore. Even the quest givers who ultimately ask for his death are saddened that it has come to that point.
Couple of other interesting things of note with VanCleef. His Armor that he is wearing in Deadmines is the Madcap's set along with his classic Red Defias mask.