The League of One was one of the salarian intelligence services at the time the salarians discovered the Citadel. Their primary training was in espionage and assassination. Never more than a dozen strong, the team was adept at infiltrating the tightest defenses and eliminating all necessary obstacles.
Only a few top members of government and military were privy to the League's identities. League members wore no distinguishing garments, and held no particular rank. The only evidence of their participation in the League was a small medallion presented to each member upon induction. This secrecy was maintained until the formation of the Citadel Council.
In an effort to dispel rumors and appease their new asari partners, the Salarian Union released all classified documents pertaining to the League. The League of One was suddenly exposed and in danger of being hunted by the enemies of the salarians. Before any harm could be done, the team mysteriously disappeared. Most assumed this was a convenient lie to help hide their identities, but a few months later, the inner cabinet was murdered. Though there was no incriminating evidence, it was clear who was responsible.
Realising the threat posed by this rogue outfit, the Special Tasks Group dispatched a team of hunters. When they didn't return, the STG dispatched ten of its brightest military operators with broad discretionary powers, resembling the deployment of Spectres. Only two returned; they reported no evidence of the League.
No further incidents were reported and it was assumed the League was wiped out. Some recently declassified documents, however, have suggested there may have been a thirteenth member who eluded the salarian military.
League of One medallions have been found in escape pods (such as the one on Rayingri), on an abandoned fighter (found in an asteroid belt in the Knossos system), on a collapsing space station (Gromar) or hidden within probes (Yunthorl). One, on Nepmos, may have been buried. Another may be found on a mummified salarian corpse (Klensal).