The Kingsguard or Queensguard, also known as the White Swords or White Cloaks, are an elite royal group of seven knights, supposedly the greatest and most skilled in Westeros, who serve as the royal bodyguard of the Lord of the Seven Kingdoms. Their duty is to protect the king and the royal family from harm at all times. The Kingsguard swear the most holy of vows to fulfill their sacred duty, and - in theory - are meant to be the living exemplars of the pinnacle of knightly values. Like the Night's Watch, Kingsguard vows are taken for life, and members can only to be pardoned by royal decree (although even this is frowned upon) or through death.
The Kingsguard has severely depleted in quality since the fall of Aerys II. His kingsguard was virtually decimated, with Robert replacing the gaps left with less-than-elite knights. Ser Barristan and Ser Jaime were all that remained: the rest were knights of dubious integrity and skill.