When the peasants of Ba Sing Se rebelled and gained control over the whole city excluding the Royal Palace, the King's guards barricaded themselves in the palace, determined to protect him until the bitter end. However, unable to handle the revolt and fearing for his life, the Earth King summoned AvatarKyoshi to the capital to aid him and bring the revolt to an end, but she refused. The tyrant was furious about the fact that Kyoshi, an Earth Kingdom citizen, dared to defy her king, and promptly ordered her arrest. The Royal Earthbender Guards obeyed without hesitation, but proved to be no match for the Avatar, as she easily brushed them aside with airbending.
Around 270 years later, in 0 ASC, the Fire Nation instigated a war that would last a century. The Earth Kingdom was invaded and the Royal Earthbender Guards soon became the first line of defense for Ba Sing Se: protecting the capital to protect the Earth King.
In the spring of 100 ASC, the Royal Earthbender Guards, under the command of General Sung, tried to fight off the Fire Nation drill that assaulted Ba Sing Se. However, Sung ordered the guards to throw boulders on the heavily armored drill which proved ineffective. The aid of Team Avatar eventually secured the victory for the guards.
Later on, the Royal Earthbender Guards attempted to prevent Avatar Aang and his team from reaching the 52nd Earth King, Kuei. They used specialized surface-to-surface rocks against the invaders, re-purposing the projectiles as surface-to-air rocks against the airborne bison of the Avatar. Nevertheless, they were quickly defeated by the elite force who then broke into the palace complex.
When the Avatar tried to convince the Earth King about a conspiracy that prevented Kuei to be informed about the war, the King's Guards escorted Earth King Kuei while he toured around the city with Team Avatar.
After the Hundred Year War, the King's Guards continued their duty, and when the Harmony Restoration Movement failed and the crisis regarding Yu Dao escalated, they served as sub-commanders of the Earth King's army in the ensuing battle against the reformed Fire Nation Army. When the battle eventually ended with a ceasefire and a temporary agreement, they, along with Earth King Kuei and General How, returned to Ba Sing Se peacefully.
They sported a uniform different from that of a normal Earth Kingdom soldier, wearing heavier, dark green armor with a green plume on top of the helmet. Their clothing seems to be heavily inspired by the Qing Dynasty brigandine armor.