Sentinels are a group that appears in the Sonic the Comic series published by Fleetway Editions. They are powerful stone robots created and employed by the Drakon Empire as soldiers and guards. Like all Drakon warriors, they often wield powerful energy weapons. In battle, they are sometimes led by a Drakon Prosecutor. Despite their power, however, Sonic has commented that they are not much tougher than regular Badniks.
Most Sentinels are an average human height, two or three times as tall as Sonic. Some Sentinels, known as Master Sentinels, are far larger. Sonic is about the size of a Master Sentinel's finger.
When the Drakon Empire withdrew from Mobius, one giant Sentinel that had been stationed in their Aquatic Ruin Zone outpost was caught in a tremor and trapped under the lake as the city sank. It remained undisturbed for over two thousand years before another earthquake caused it to resurface. When Sonic the Hedgehog came to the Aquatic Ruin Zone to investigate, he was trapped on the lake bed under some columns, and would have drowned if the Sentinel had not reactivated and saved him. However, having learned that its masters had deserted the city that it had been built to protect, the Sentinel destroyed itself. (This was presumably a Master Sentinel, although it was never named as such in the series.)
Many years later, after Dr. Robotnik was captured by a Drakon Prosecutor for tampering with a Mobius Ring, Robotnik informed Emperor Ko-Dorr of the Sentinel's destruction, having seen it through a spy camera. Sonic was brought before the Emperor and charged with the crime of destroying the Sentinel himself, although he later "proved" his innocence in a death match and was released.
When Ko-Dorr visited Mobius, hoping to discover the location of the Chaos Emeralds, a Prosecutor led several Sentinels (including a Master Sentinel) to the Emerald Hill Zone to capture Sonic and learn from him where the Emeralds were hidden. Sonic and Tails managed to destroy the normal Sentinels, but the Master Sentinel was significantly stronger. Sonic eventually defeated it by creating a hole in its armour, allowing him to climb into the robot's chest cavity and pull out all of its mechanical components.