Sentinels are the walking tanks.
These close combat powerhouses use their fists to beat the opposition into submission. Sentinels can soak up a lot of damage with their heavy armor, and their high HP means they can take a beating and still keep on coming. They loom larger than life on the battlefield, giving enemies a giant target they can focus on while the rest of his or her squad tear them apart one by one.
For a Sentinel, all they need to take you out is their bare hands.