Genbu Kururugi is Suzaku's late father, the last prime minister of Japan, and host for both Lelouch and Nunnally Lamperouge seven years prior to the beginning of the series.
SpoilerBefore the beginning of the series, Genbu Kururugi was the Prime Minister of Japan and the father of Suzaku Kururugi. He later receives Lelouch and Nunnally as hostages. When Britannia began its invasion of Japan, Genbu refused to surrender, preferring unending resistance against Britannia. It was reported in the media that Genbu Kururugi had committed suicide in order to stop the all-out war against Britannia.
The only other times Genbu was seen, was during flashbacks and when C.C. transmitted memories into Suzaku during the Battle of Narita.
After Suzuku and Lelouch save Nunnally from Mao, Suzaku planned to arrest Mao. However, in order to get a chance to escape, Mao uses his Geass on Suzaku. He reveals that Genbu Kururugi was actually murdered by his own son. He planned on a do or die resistance, however Suzaku killed him believing that it would stop the war. In the aftermath of that incident, the truth behind Genbu's death was covered up in order to protect Suzaku.
Code Geass Wikia
