Legion is the name taken by the gestalt consciousness formed by 1,183 geth programs inhabiting a unique geth "mobile platform".
Discovery by Swindle and Integration into the Criminal Empire.[]
A deactivated Legion laying with an army of Geth were founded by Swindle and his Vehicon Drones to be taken away and sold to his master, the Kingpin, for more money to bring in additional enforcers for the Criminal Empire.
LOTM: Darkness Incarnate[]
Legion survived dispersing the code and became a full functioning individual with a life of his own than just a bunch of computer programs. With full sentience on, Legion refers himself as I instead of we.