The Guard troops, also known as Frieza's Honor Guard, are a group of Frieza Force members who served under Frieza and Cold's direct command, and also as the elite personal guard of Frieza himself.
The guard troops were not present at the time of Cold's death and Frieza's first death. They were unaware that the Z Fighters even existed, only being aware that Frieza and Cold had been killed upon invading Earth, after having the planet scouted and discovering the "strongest man" Mr. Satan they chose not to invade until he was dead, as they knew they could not deal with the one who defeated Frieza.
After Mr. Satan's death, the guard troops finally ordered the invasion of Earth in Age 820, leading to a full planet wide conflict and many deaths, and finally culminating in a battle between the aged Z Fighters and the Galactic Frieza Army, presumably, the guard troop were defeated and possibly killed during this conflict, though some survived to continue operating as leaders of the army when it went into hiding on Earth.
In Age 1000 the Frieza's Force remnants still existed under the command of surviving guard troops, they joined the Time Breakers with the goal of reviving Frieza once more using any parts of his body they could find in conjunction with their upgraded regeneration technology.
It is stated by Frieza that an individual member of the Honor Guard should be able to defeat the entire Ginyu Force, and must fight to their last to protect Frieza. In order to test worthy candidates for the Honor Guard, Frieza personally faces them in both his first and fourth forms in order to prove that they possess enough power.