General Grievous

General Grievous was a cyborg Separatist military leader who was responsible for the prolonging of the Clone Wars, as well as hunting many Jedi.

Grievous was originally a Kaleesh Warlord who later underwent Cybernetic enhancements when he became a General for the Separatists

Turmoil on Kalee
Grievous's homeworld was Kalee, a planet in Wild Space on the fringe of the Outer Rim which had continuous fighting between the war-prone Kaleesh tribes. Grievous was a Warlord who was revered amongst his people for triumphing against an oppressive and technologically advanced species called the Huq which sought to enslave the Kaleesh. Grievous lover died in these wars which is where he took on the name Grievous to represent his feelings of sorrow. His anger made him become a more savage Warrior, where he butchered populations of the Huq who remained on Kalee.

Offensive Against the Huq / Republic Intervention
His revenge was furthered when he sought to go beyond the Huq colonies on Kalee and commit a genocide on all Hux in Wild Space. He was successful to the point of nearing the home planet of the Huq when the Huq government called in the Jedi for aid in combatting Grievous's horde. Sanctions were also placed on Kalee which led to many deaths from starvation on Grievous's homeworld. These events are what fueled Grievous's hatred for the Jedi and the Republic.

Shuttle Accident / Cybornetic Reconstruction
Grievous's success sparked Darth Sidious's interest in his skills as a general and tasked Dooku to enlist him to lead the Separatist armies. Dooku orchestrated a shuttle accident for Grievous which badly damaged his body. He blamed the attack on the Jedi and the Grievous was rebuilt as a Cyborg via the technology of the Intergalactic Banking Clan. Grievous was predominantly machine from there on out, with his only organic parts being his brain, heart, and eyes.

Training from Count Dooku
Grievous was trained by Count Dooku, not only in the physical realm of Jedi lightsaber combat, but in the psychological side of combat. Dooku taught Grievous how to break a Jedi's concentration and will-power by striking terror into his targets.

First Reveal on Hypori
After his army downed an Acclamator class cruiser, Grievous picked of all Republic troops, leaving only a handful of Jedi left. Jedi Master Barrak had just enough time to contact Obi-Wan Kenobi (who had just finished the campaign on Muunilist) to call for help before being killed by Grievous.

Grievous then stalked the last of the Jedi task force, surrounding them by legions of super battle droids. He taunted them, his voice echoing through the rafters. The most high-ranking Jedi was Ki-Adi-Mundi who urged his compatriots to stay calm, but the Padawan Sha'a Gi preemptively rushed out to confront the droid general. Grievous landed on Sha'a Gi and began fighting the Jedi. He either killed or incapacitated all the Jedi, save for Kiadi when a squad of ARC Troopers led by Captain Fordo were dispatched to retrieve the Jedi. Their immense firepower sent Grievous on the retreat. Kiadi opted to pursue, but Captain Fordo informed him that the survivors were in critical condition. Only Jedi Masters Ki-Adi-Mundi, Aayla Secura, and Shaak Ti, the latter two badly injured, survived the encounter with Grievous.

Kiadi would soon after bring up to Jedi Council the issue of Grievous and his proficiency in fighting Jedi."'When was the last time someone fought five Jedi... and held there own!' - Ki-Adi-Mundi to the Jedi Council addressing the threat of General Grievous after their encounter on Hypori"

Outer Rim Offensive
Grievous was an exceptional General and won many victories in a massive Separatist offensive towards the end of the Clone Wars, stretching the Republic's forces thin across the Outer Rim to contain his offensive. This left the Republic Hyperspace lanes vulnerable to an attack on the Galactic Capital.

Also, in relation to Palpatine's master plan in the eradication of the Jedi this move left many of the best Jedi far from Coruscant and the Jedi Temple.

Last Stand on Utapau
...

Grievous met his match with the clever Obi-Wan Kenobi. Obi-Wan was grievous as like a puzzle, being a non-force user Grievous could be solved for the patterns he used and broken

References