The Death Watch were a splinter group of Mandalorians who were first defeated by Jango Fett in 34 BBY and later resurrected thanks to the help of the revived Emperor Palpatine. They began a war to destroy the New Republic by first invading Onderon in 18 ABY. They began to take subsequent planets for their cause.
Its members, under the leadership of Tor Vizsla, fought against Jaster Mereel's "True Mandalorians" during the Mandalorian Civil War. They opposed his reforms and wished to continue to be savage raiders. At least some of them, including Vizsla, wished to start a new Mandalorian War and conquer the galaxy. They wore unique helmets and were led by an "Overlord." When Jango Fett finally defeated Vizsla, the remaining members of the group scattered, and it ceased to have any influence on the galaxy. That changed around 22 BBY when Pre Vizsla took command of the Death Watch. The group then battled the Republic until Spar had the group join into his Mandalorian Protectors. A splinter of the group would hide on Endor well into the Galactic Civil War.
Defeat and revival
Around 1 ABY, a team was sent to Endor to wipe out the Death Watch. Horatio Theta, a Mandalorian from Dxun was apart of the team. The team was successful and the Death Watch were removed from the galaxy. Fifteen years later, Horatio would name his Mandalorian organization the Death Watch, as he felt they had the same ideals as the original group.