The Mandalorian Protectors were the branch of Mandalorians founded by Mandalore the Resurrector, a rogue ARC trooper, during the Clone Wars. The first group of Protectors numbered 212.
In 20 BBY, the Protectors were defeated at the Battle of New Holstice. Shortly afterward, a number of them were apparently massacred by their allies, the Geonosians, at Zaadja, and suffered another defeat at the Second Battle of Kamino. At the end of the Clone Wars, all but three perished, but Fenn Shysa reformed them again when he became Mandalore.
Unlike the Mandalorians of old, who were crusaders facing various other races for honor, these Mandalorians simply protected the borders of the Mandalore Sector and the Mandalorian people as a whole. However, they would also protect the Galaxy itself if they felt the need, as they did under Fenn Shysa when they helped defeat the forces of Lord Shadowspawn in the Battle of Mindor.
Under Boba Fett, the Protectors initially chose to ally with the Yuuzhan Vong in the first months of the Yuuzhan Vong War, under the lure of the immense amount of credits offered by the invaders. To this end, Fett initiated a brutal training regimen for his forces on Raxus Prime, killing many of them. Fett, however, fully expected the Yuuzhan Vong to break their word, and used his place to feed information to the New Republic. By the last year of the war, the Protectors had switched sides, possibly due to the end of Vong payment or a (possibly subsequent) attack on Mandalore, and fought at several worlds in the Outer Rim Territories.