Death Eaters are dark wizards gone bad. They are part of Voldemorts army. There have been several accounts of death eaters. They were originally called "Knights of Walpurgis." They caused many, many battles. The main reason they formed was to dominate over the wizarding world with their true master Voldemort.
In the SkyEdit
Death Eaters have their own Dark Mark . It was banned by the ministry, because it symbolized that someone has just been killed, and the owner of the wand casted can be sent to Azkaban for life. The spell is Morsmordre. A skull comes out in the sky, and a snake comes out of the mouth calling Voldemort and the Death Eaters.
On the ArmEdit
Many Death Eaters, have the mark on their arm. It is likely only given to Pure bloods who are death eaters. It is a mark of a Dark Skull with a snake coming out as the tongue. The person who wants to call on Lord Voldemort touches the mark with his/her wand .