The Brotherhood Mortalis was a powerful mercenary brotherhood, a large network.
The Brotherhood Mortalis was the biggest organization of its kind, with up to 20,000 members spread across a hundred worlds. Many local governments and even smugglers hired only Brotherhood members, trusting the organization's reliability. Like other brotherhoods, it wasn't a tightly organized military power, but a loose network of contacts and contract makers that provided a measure of camaraderie among its members. The Brotherhood's principles responsible for its success were simple: when a member identified himself, provided it was safe to do so, another Brotherhood member would lend medical aid. This simple pact, although rarely taken to the extreme, made members less likely to flee armed conflicts and more reliable to their employers.
The brotherhood was formed in 25 BBY, three years before the Clone Wars. Later, in 1 ABY, the Dark Jedi Lord Vartonis hired Brothers of Mortalis to help him obtain the powerful on the volcano moon Mustafar. Many of them were killed during futile attempts to prevent a spacer from gaining access to the Lair of the Crystal.