Thief, About

"Experts at stealth and surprise, thieves can move through the shadows, vanish into thin air, or steal items from their opponents and use them as weapons. Thieves practice an agile, acrobatic fighting style, which can make them very hard to hit"

Thieves are expert in the shadow arts. They utilize stealth and shadowstepping to surprise and to get close to their target. They're deadly in one-on-one combat using their agility, acrobatic fighting style, and the ability to steal to overcome their enemies. They have an affinity for setting traps and using venom. As an adventurer profession, thieves wear medium armor.

http://metabattle.com/wiki/Theif
http://wiki.guildwars2.com/wiki/Theif