Terran Guard

The Terran Guard, also known as the Obsidian Guard is an elite Terran unit whose members serve as personal bodyguards to Terran officials. Higher officials, such as Councillors and the Chancellor are almost never seen without their personal guards. The total number of guards varies, but usually is around ten thousand. The number of guards assigned to a person also varies drastocally, from one or two for Senators and Legislators (Assembly members) to up to two dozen for Councillors and the Chancellor. The Guard is a part of the Terran Armed Forces, but guards only answer to their assigned target. 
Guardsmen are trained on New Rome in the Sirius system. The training complex is located in the Great Wasteland near the south pole of the planet. Guards are recruited among soldiers, most often from the Army or the Ultramarines with at least five years of experience. As most guards would be assigned to Senators and Legislators, their training would last around a year. More experienced guards would be assigned to Governors, Administrators and TA Council members. The most elite guards, often recruited amongst orphans at a young age and trained their entire lives, protect the Chancellor and the Councillors. They're oftened referred to as praetorians. 
The Guard was founded in 2079 by the Custodian to serve as his personal bodyguards. During his reign they prevented over fifty assassination attempts. In the immediate aftermath of his resignation the Guard persisted, but only for a short time. They initially served only to protect the Chancellor and Councillors. As time went on and the number of assassination attempts decreased, plans were made to disband the Guard. In 2129, the Commander of the Guard launched a coup which was ended in little over four hours. The Guard was disbanded. During the First Contact War however, an alien sympathiser shot Chancellor John Hu. The Guard was promptly reestablished and its role expanded to most Terran officials