CLU 2, which stands for Codified Likeness Utility 2.0, is an artificial intelligence program that was written by Kevin Flynn.
CLU 2 looks virtually identical to a younger Kevin Flynn, his creator, as well as his predecessor, CLU, who was killed in the original Tron. At first, CLU 2 wears the same garments as Flynn - a black leather jacket with a glowing white zipper and jeans - but following his coup d'etat, he dons a much more sinister uniform consisting of a black skintight suit with orange circuitry similar to Rinzler, a colour shared by the Tron universe's villains.
An earlier version of CLU existed during the events of the original TRON film in which he was used by Kevin Flynn to hack into the ENCOM mainframe and collect evidence of Ed Dillinger's plagiarism. But CLU was captured by and derezzed by the Master Control Program.
Before TRON: Legacy, A new version of CLU was created by Kevin Flynn when he created a new version of The Grid. Flynn promised to CLU 2 that they would help create "the perfect system," a goal CLU 2 never put to rest. Especially when the spontaneously created programs called ISOs (short for "Isomorphic Algorithms") came into being. Kevin saw them as a miracle, whereas CLU saw them as an imperfection. In determination to rid all imperfections, he killed all the ISOs (in an event known as "The Purge") not only reprogramming Tron into Rinzler, but also forcing Kevin into hiding within the Outlands of The Grid for 20 years.
In TRON: Legacy, CLU 2 continues to carry out the execution to shape a perfect system, reprogramming innocent programs into soldiers and creating an army to infiltrate the real world. He lures Sam Flynn into the Grid and attempts to kill him until Quorra comes to Sam's rescue and takes him to his father. CLU 2, still unaware of where Kevin is hiding, decides to use Sam as a pawn to lure the Flynns out of hiding in order to obtain Kevin's disc that would provide passage through the portal to the real world. When CLU 2 finally has all of the pieces in place, he attempts to transport his army via a warship, the Flynns along with Quorra escape with Kevin's disc on a Light Jet. CLU 2 pursues them in his own jet with Rinzler and a squad of guards behind him. Rinzler, who remembers his identity as Tron, crashes his jet into CLU's. After a slight struggle, CLU 2 knocks Rinzler off and chases after the Flynns, leaving Tron to drown in the Sea of Simulation. After a final confrontation, Kevin executes a reintegration sequence to absorb CLU 2, destroying them both, allowing Sam and Quorra to escape to the real world.