The Jedi Temple Guards were part of the Temple Security Force, a sect of Jedi that scrubbed away their past identities and devoted their whole lives to protecting the Jedi Temple and the Jedi Order.
They were led by Cin Drallig, a Jedi Master and wore special robes with armor plates and a mask, they also had special Lightsaber pikes with a yellow blade. Unfortunately, most of the Guard was wiped out when Darth Vader and the 501st, a clone trooper legion, attacked the Temple, and it is unknown if any of the Guards survived.
During the Clone Wars, Jedi Temple Guards were responsible for guarding the Jedi Temple on Coruscant. Later, several Temple Guards intervened in a lightsaber duel between the Jedi Knight Anakin Skywalker and the rogue Padawan Barriss Offee. After Barriss was exposed for framing Ahsoka Tano, several Temple Guards led her into custody.
The Temple Guards, along with the entire Jedi Order, were presumably targeted for destruction by Emperor Sheev Palpatine during Order 66. The Grand Inquisitor, a Pau'an who headed the Galactic Empire's Inquisitors, was once a former Temple Guard and Jedi Knight. Years later, several spectral Temple Guards including the Pau'an who became the Grand Inquisitor appeared in Kanan Jarrus's Force vision at the Jedi Temple on Lothal. After dueling with him, the spectral form of the Pau'an Guard knighted him as a Jedi Knight. These spectral guards later delayed the Inquisitors known as the Fifth Brother and Seventh Sister; allowing Kanan and his companions to flee into hyperspace aboard the Phantom.