The Vahzilok are a "gang" that operate in the City of Heroes MMO.
Picture an army of undead monsters put together from parts scavenged from graveyards. They want your brains... and your liver, your lungs, your spleen, your arms, legs, and pretty much everything else. Not to eat, of course, but to make more of them.
There are two kinds of Vahzilok members... the living and the undead.
The undead minions are the semi-mindless foot-soldiers. They have all been put together by pieces of dead bodies dug up from graveyards or harvested from freshly-killed victims.
Because they were dead, they cannot feel pain. They do not care what happens to their bodies. They only do what they are told to do.
The undead have three kinds of weapons. They have their physical strength, which is slightly stronger than normal humans because there is no pain tolerance. They also have projectile vomit, which not only leaves a lasting stench on the victim, but also corrodes the defenses of a person. And some minions have bombs strapped to their backs so they can explode and kill their victims (and everything else in the immediate range).
(Note: for some reason, only male cadavers are considered "worthy" to be undead minions.)
The living include those who were dead briefly so they could be brought back with enhanced abilities.
Some of the living minions are disgraced doctors and medical students. They're the ones that put the undead minions together, and they're also the ones that can bring those minions back up when they are defeated. They carry bone-saws and cleavers with them along with just enough of their chemical "cocktail" to bring the dead back to un-life.
Then there are the Eidolon. These are people who were living, then killed just long enough to be enhanced with superhuman and dark abilities and then brought back to life. They are formidable by themselves, but when combined with the other members of the Vahzilok faction, they pose a serious threat to any one hero.
(Note: There are both male and female Eidolon.)
(See also Dr. Vahzilok)
The leader of the group that bears his name is not just the leader, he's also a client.
He's augmented himself with parts of other bodies, including large Vahzilok minions, along with a huge gunship cannon to make himself stronger. So strong, in fact, that only one hero was ever able to defeat him alone: Galatea Powers.
Impact on Paragon City
Unlike other criminal organizations, where the impact seen in a community is in fear and degrading property values, the Vahzilok have a unique effect on life in Paragon City. Because they get their "recruits" from the dead, the Vahzilok have an emotional impact on the memories of the loved ones.
Imagine seeing the Vahzilok robbing a bank or attacking a store opening and seeing your dearly departed father or brother as an undead minion. Or hearing that the grave of your grandfather was broken into and your grandfather's body was now being used for spare parts.
Because of this, burials were prohibited in Paragon City. All dead bodies have since been cremated.
(See their Paragon Wiki entry for more information.)
The Vahzilok were seen in "The Guardian Powers" #10.