History
Grievous in Legends is a master warrior who craves the challenge of honorable combat. Padawans and younglings are beneath him, as he craves the hunt, not the catch. He is worshiped on his planet as a demi-god and him and his lover/best-friend protected their world from invading forces for several years. While he was a master of the rifle and an expert sniper, she was a master of the sword, and together they fought to free their people from the oppression of an invading race (the Huk) while the Jedi did absolutely nothing to stop the Huk from the genocide of the Kaleesh.
The two became very close before her tragic death at the hands of the invading aliens. Utterly heartbroken, Qymaen jai Sheelal (as he was called back on his homeworld) renamed himself Grievous "For the wound that shall never heal" and turned all his anger and sadness toward the Huk, swearing to honor his beloved by using purely bladed weapons, and to never using ranged weaponry again.
Aided by his elite Kaleesh Guard, whom he trained himself he forced the Huk off Kalee and then swarmed their homeworld, conquering them and disbanding their military. THEN during his flight back to Kaleesh, where he planned to put down his blades and rebuild his people's homes, his ship is blown apart and all of his friends are killed, himself barely surviving with heinous injuries that would permanently maim him.
After being brought from the brink of death by Dooku who sought to invite Grevious to the confederacy on the account that the Republic watched his homeworld burn and have never done anything for Kalee, Dooku revealed that it was the Jedi who destroyed his vessel, who were under the belief that Grevious and his elite guard were terrorists who had attacked the Huk homeworld.
It is implied that the Huk leaders themselves were in on the plot, as they wanted revenge against the one who had almost single-handedly ruined their war effort with guerrilla tactics and psychological warfare.
Overcome with grief and rage that his lifelong companions had all been killed for what essentially equated to "faulty info", Grievous swore he would kill every Jedi he could get his hands on, and bring the Republic to its knees. Of course, we know that Sidious orchestrated the bombing of Grevious's shuttle in order to turn his anger towards the Republic, after all Grevious had conquered his enemy, he had no reason to fight in the clone wars. A peaceful warrior is useless to Sidious, so he bombed the shuttle, and framed the Jedi.
Grievous's cyborg body was also built to dull his senses, lower his wits, and heighten his aggressive tendencies. Sidious and Dooku both feared what Grevious would do if he ever learned the truth about the bombing on the shuttle, and took every precaution to make sure he never learned the truth. They also intentionally weakened him, made unnecessary modifications, and made sure he would be unable to use the force, which is heavily implied that he was force sensitive before his transformation into a cyborg. All in the hopes that he would become easier to dispose of when the time came to destroy the confederacy to make way for The Empire. (And yet he was still skilled enough to fight multiple Jedi at once with only half of his available arms)
The Magna Guard (the gray cloaked droids with purple lightning staffs) seen in the series are droids that have been designed to both look and fight like his Kaleeshi Elite Guard, though Grievous is quoted as saying "They are a sick imitation compared to my beloved companions of old." Grievous has taught each Magna guard himself in hopes of replicating the skill of his lifelong friends. But in Grievous's own words: "There is no fire in their hearts, they cannot learn how to fight, they know only to obey."
POST CLONE WAR / EMPIRE AGE (Extreme non-canon mode)
Surviving the duel with Obi Wan on Utapau, Grievous retreated to his homeworld of Kalee after all these years, taking his personal transport and a small troop of his Magnaguard elites. His return was a shock to his people, who believed he had perished at the hands of the Jedi. He had since been hailed as a war deity, and shrines to him had been placed in what remained of the Kaleesh burial grounds.
Grievous was sitting upon the brink of madness, effectively rotting from the inside out and clouded beyond reason. The sight was horrific, and led to him being taken secretly by a small group of Kaleesh. After the Clone wars had started, Kalee had been struck by multiple war's following their economic crisis during the Huk invasions. Sections of the planet had been conquered by off-world tyrants, and their culture was slowly being destroyed by military force, striking more and more kaleesh tribes to rise up and seek vengeance. A large amount of the Kaleesh had been sold as slaves, and bodyguards, gaining them a reputation as merciless, honorable warriors.
Grievous was placed into medical care and examined. While his body was a work of art well ahead of its time in terms of combat capability, it was clearly not designed to keep him alive. Damaged organs were being poorly maintained when they could be easily replaced with cybernetic equivalents, life support had caused intense levels of atrophy, and his mind was plagued with implants that stimulated his violent tendencies. A filter had been placed within his life support, suppressing and terminating the now highly concentrated colony of midichlorians in Grevious' nervous system. He was built to die, a fact which enraged the Kaleesh.
He was placed into a medically induced coma and went through what level of surgery the Kaleesh could afford him. After months of steady recovery, the newly restored mind of Qymaen jai Sheelal woke, meeting the galaxy that had seen the end of the Clone Wars, and his homeworld in agony.
Outraged by the subjugation of his people, and the suffering placed upon him by his former Sith masters, Sheelal swore to a campaign of vengeance to free his people and crush the Sith, a task he knew would be no small feat. After recovering his personal items secured in an abandoned fortress he had placed on Vassek, he began to train a new breed of Kaleesh warriors as a rebel force, using the many lightsabers he had collected during his conquest as General Grievous. He alone effectively revived the seven arts of saber combat after the Jedi's destruction during order 66.
Over the planet of Kalee he began his conquest, relentlessly carving the tyrannic forces from his homeworld over the course of merely 2 years. His rebel force, though small in the beginning, was constantly growing and had been trained using the dangerous Magnaguards as practice dummies alongside Sheelal's teachings. He had freed and conquered his homeworld.
He began to rebuild his society, uniting the Kaleesh tribes under the ideal that civilized space would be a source of constant war and injustice. They modernized their forces, but their tribalistic and spiritual nature had not been abandoned.
Kalee would slowly rise in power over the next decade, supplying the galaxy with mercs skilled in Jedi and Sith combat, even without the force. They fought on both sides of many galactic wars, and would repeatedly force the Galactic Empire out of Kalee space, colonizing a large sector as their own. Qymaen jai Sheelal himself had been placed as Supreme Leader, an immortal warlord god with no equal.
A warlord with a new power stirring within him, the power the Emperor had feared from the very beginning...
