Sith Juggernauts were Sith Warriors who fought for the Sith Empire during the Great Galactic War and the Cold War that followed it circa 3653 BBY.
These Sith specialized in combat endurance and were known for wearing armor that provided them special protection in battle. Sith Juggernauts were known to primarily wield one lightsaber in combat, and were frequently adept at using the Force to cause terror and despair in enemy combatants. Sith Juggernauts usually had an intense muscle build, which helped them physically when using a lightsaber or in combat.
The Sith Juggernaut is an advanced class for the Sith Warrior class in the Star Wars: The Old Republic MMORPG video game. This advanced class specializes in the use of heavy armor and greater stamina in battle. The Republic counterpart for this archetype is the Jedi Guardian. It appears the Sith Juggernaut is based on Darth Vader, due to great strength, heavy armor, single saber, and powerful Force powers. Officially though, the juggernaut is based on Marka Ragnos.