He was seen talking with Kane about the Liquid Tiberium bomb, a project that Kilian Qatar, Kane's supposed second-in-command, had been kept in the dark about. He later briefed a legendary Nod general about the Scrin Threshold Towers, adding credence to the theory that this man was an extremely important Nod officer.
Behind the scenes
The Advisor has an uncanny resemblance to an aged Anton Slavik, causing some to speculate that this was indeed the former leader of Nod. However, Kane's Wrath revealed that Slavik was assassinated by his Black Hand rival Marcion, invalidating that theory.
Inner Circle advisor appears in some of the Tiberium Wars cutscenes.