Christos Sevon is a Greek diplomat from the United Nations.
When French diplomat Rene LaPointe orders security to escort HydroCorp engineer Maria Martinez out of a party after she confronts him with proof that her assistant and lover Omar Risha is not a terrorist like the UN believes him to be, Sevon appears and takes her with him. He offers her his help to her.
Maria is eventually able to discover with Shaw's help that the letter stating that Omar is a terrorist was forged by Ken Davis and enlists Sevon's help to break into Lapointe's office. Maria is able to find the real letter and when Lapointe enters, Sevon murders him. Sevon reveals himself to be a former member of the French Foreign Legion and Davis' partner in stealing the hydroelectric generators. Before he can murder Maria as well, he is interrupted by Reese, Fusco and Omar and forced to disarm himself by Fusco. Reese then reveals they found proof of Sevon's corrupt activities: a customs form for the generators at the Iraq-Turkey border signed by Sevon and discovered by Finch on the HydralCorp Intranet. Sevon attempts to attack Fusco with a knife but Fusco dodges his attack and punches him and Maria knocks Sevon out with a bowl to the head.
Fusco later tells Omar and Maria that Greece has revoked Sevon's diplomatic immunity, allowing the NYPD to arrest him for the murder of Lapointe.