Wickham's name is no coincidence for he is, indeed, "wicked".
As Darcy explains to Elizabeth,
Mr. Wickham is the son of a very respectable man who had for many years the management of all the Pemberly estates; and whose good conduct in the discharge of this trust naturally inclined my father to be of service to him; and on George Wickham, who was his god-son, his kindness was therefore liberally bestowed.
We know that Wickham was supported by Darcy's father to even attend college at Cambridge. However, all it did for him was make him a master of illusions, and a deceitful traitor with the charm and manners that could fool everyone.
Ad the death of Mr. Darcy (the father) Wickham's true colors came out. He refused to take on any profession of which Mr. Darcy Senior would have liked, and he demanded that Mr. Darcy (the son) would support him monetarily in the pursue of other goals. This, he did with premeditation and haughtiness, using the affection that Old Mr. Darcy had for him as a way to shove it to the Young Darcy, who always figured as much.
On top of it, Wickham proposed himself to Darcy's sister Georgiana, and they eloped. Using the same charm and wit, he convinced her of a lot of follies, and she fell for it only to be saved in reputation later by young Darcy.
In addition to that, he did the same thing with Elizabeth's sister Lydia. Lydia, who already was the closest thing to a bubble head, was infatuated with men in uniform and with the idea of marriage. Wickham proposed that they also eloped, which she did, ruining her reputation and their chances in society. Darcy intervened one more time by finding them in Brighton and marrying them off, which allowed Lydia to return with her head held high (and very snobby too).
The biggest prroblem with Wickham is that he poses to be, as Elizabeth says, "the most agreeable man" when, in fact, he is deceitful, ambitious, immoral, and careless. He did not love any of the women he eloped with, and his effrontery as a military officer was just a way to attract people into thinking that he was an honorable man.