The League of Doom, also referred to as the Legion of Evil, is a "super-villain" group created and lead by Sue Sylvester, whose main objective was to destroy The New Directions, and help Vocal Adrenaline win Nationals.
When first created, the group had 3 members beside Sue Sylvester: Vocal Adrenaline coach Dustin Goolsby, previous Glee club director Sandy Ryerson, and Will's ex-wife Terri Del Monico, though later Howard Bamboo joined as well. Several people such as Azimio Adams, Becky Jackson and Jacob Ben Israel were involved in missions of the League intentionally; while others, notably April Rhodes assisted them unknowingly.
The first five people to join have codenames: Sue is 'General Zod', Dustin is 'Sergeant Handsome', Sandy is 'Pink Dagger', Howard Bamboo is 'Panda Express' and Terri Del Monico is 'Honey Badger'.
Break-up Will and Holly
The first mission of the League was led by Dustin Goolsby, and its objective was to get Holly and Will to break-up. Though Holly did eventually break-up with Will, Dustin didn't have anything to do with that, which made Sue deem this mission a failure.
Mission by : Dustin Goolsby
Status: Succeeded (seen as a failure by Sue)
Destroy the "Night of Neglect"
Sandy's first mission was to use the "Heckling club" to make sure the "Night of Neglect" benefit was a failure, therefore preventing New Directions and the decathlon team from going to their respective National tournaments. As possibly the worst failure of any mission of the LoD, this one ended, not only with the Hecklers leaving after a talk with Holly, but also with Sandy funding the decathlon's trip from his drug profits.
Mission by : Sandy Ryerson
Re-instate "The Muckraker"
Inspired by "Wikileaks," Sue used McKinley's old newspaper "the Muckraker" to spread rumors about Glee Club members and create tension within the group. Though this mission didn't have a great influence on the Glee Club after Rumours it is the League's only successful mission, as it did cause tension within New Directions and it helped their next mission: to get Will to quit.
Mission by: Sue Sylvester
Get Will to quit
An ongoing mission by the League is Sue's and Terri's attempt to get Will to quit teaching at McKinley in favor of doing "Crossrhodes" on Broadway with April. Even though Will refused April's offer to take the show to Broadway with her, and said that he wouldn't be leaving the Glee club for a stage career, he later admitted to actually take part in April's show, though still not quitting McKinley.
Mission by: April Rhodes
Send the Glee Club to Tripoli
Possibly the League's only successful mission, Sue, Terri and Howard succeeded in exchanging the Glee club's tickets to New York with tickets to Tripoli, Libya, although since Sue and the Glee club aren't enemies after the events of Funeral, she and Terri replaced their tickets with new first-class ones. (Please note that this was around the time that the protests against Moammar Qadaffi were being held, with many fatalities. Therefore, if the mission had succeeded, the New Directions might have died.)
Mission by: Howard Bamboo