The Imperial Senate Sentinels were a subdivision of the Imperial Senate Guard who served Emperor Palpatine. They were charged with protecting the Jedi Temple on Coruscant from looters and specially trained to combat and kill Jedi. In 2 BBY, they were encountered by the Sith apprentice Galen Marek.
The Sentinels were a subdivision of the Imperial Senate Guard and dressed similarly to the Royal Guards, but their armor and robes were gray and white rather than red, and their helmets resembled those of late Clone Wars-era Senate Guards. They wielded powerful force pikes that could effectively block a Jedi's lightsaber, which aided them greatly in their work. They had robotic voices and were thought to be cyborgs. Although the Imperial Senate Sentinels were not formally members of the Imperial Military, they have at times worked alongside them if the objectives were important enough to require their presence, including the guarding of the remains of the Jedi Temple.
The Sentinels were handpicked by Palpatine to guard the Jedi Temple on Coruscant. Once there, they watched over the ruins and protected them from looters and those who sought to plunder the secrets of the Jedi Order. Their true purpose, however, was to wait for any returning Jedi, and those that came would be attacked and killed. In 2 BBY, Darth Vader's Sith apprentice Galen Marek came to the Jedi Temple multiple times to further his training, whereupon he was attacked by a number of Imperial Senate Sentinels. Despite putting up a valiant fight, many of the Sentinels were killed in the struggle. Although during the second encounter with Marek, they attempted to warn him that he was to be detained as the Emperor had declared a quarantine at the Jedi Temple, by the time of his third and final visit, they ended up attacking him pre-emptively without even bothering to give a warning.
The Imperial Senate Sentinels made their first appearance in the first trip to the Jedi Temple in the Playstation 3 and Nintendo Wii versions of the Star Wars: The Force Unleashed video game. In the game, they were only referred to as "Imperial Sentinels," not to be confused with the Imperial Sentinels who guarded Palpatine's Citadel on Byss. They were given a proper name and revealed to be a sect of the Imperial Senate Guard in the 2009 RPG supplement Galaxy at War.