Cyborg, Jedi-killing leader of the Separatist's Droid Army
General Grievous was an infamous warlord of his native Kalee. Back on his homeplanet he gained a reputation for the successuful war campaigns he led against his peoples long-time neimesis', the Huk. Following a near fatal crash while onboard his spaceship, Grievous was given the opportunity by the Separatist San Hill to be rebuilt with a new cyborg body along with a new calling...as leader of the Separatist's Droid Army. Grievous accepted the offer and was reborn into the twisted alien/cyborg hybrid that became feared throughout the galaxy for his nasty penchant of using his Sith-training to slaughter Jedi and take their lightsabers as trophies.
While on Xagobah hunting down Wat Tambor, Boba encountered the Droid General and his bodyguards who were there to protect the Techno Union Foreman. Using a holoshroud given to him by Ygabba, Boba disguised himself to look like Durge, not that it helped as Grievous gave the order for him to be destroyed. In pain from his battle with the bodyguards, Boba did the best thing he knew to do and faked his death by using the Xabar fungus to produce it's death-like effects.
Source: "Boba Fett - A New Threat" by Elizabeth Hand