Introducing the Thief

 

A master of stealth and surprise, the thief is deadly in single combat—particularly when catching enemies off guard. Thieves compensate for their relatively low armor and health by being quick and evasive. They can move through the shadows, vanish into thin air, or steal items from their opponents and use them as weapons. Enemies should watch their backs, or the thief will watch it for them.

While other professions rely on recharge rate for their weapon skills in combat, thieves rely on Initiative. Thieves have ten points of Initiative to use, and they gain back one point every second. Weapon skills cost Initiative points, but they have no recharge time, so thieves can use them back-to-back. This allows the thief to keep their options open at all times or unleash a rapid flurry of powerful attacks.

http://www.guildwars2.com/en/the-game/professions/thief/