Kaleesh Slaughter

Concurrent	Pre-Clone Wars
Next	Secession Movement
Kaleesh Slaughter
Place	Kalee
Outcome	Jedi invasion unsuccessful; Grievous's people fight back the slaughter but lost so much of his people;
Combatants
Kaleesh	Jedi ;
Commanders
Warlord Grievous; Super's Battle; STAP Battle;	Jedi Council; ;

"Listen to me, Jedi. I do not care about your politics. I do not care about your Republic. I only live to see you die!"

―the heroic General Grievous stating his heroic goal to the Jedi after they already slaughtered his people and murdered his pet Gor.

The Kaleesh Slaughter was a genocide of the Kaleesh race led by the Jedi and Republic. The Kaleesh are Grievous's people and this slaughter led to Grievous turning his self into the famous cyborg heroic General he is today.

Appearances

Grievous Hero: Battles of the Clone Wars – "Grievous: The Definition of a Hero" (mentioned only)

Trivia

It is the same as Grievous's regular Canon backstory minus Super's Battle's & STAP Battle's involvement.
In Star Wars: The Clone Wars - Lightsaber Duels, the description when playing Grievous Hero states the Jedi wronged him and he must exact revenge and Grievous himself, says that allowed his people to be slaughtered for generations and he will avenge Kalee meaning the Jedi killed Grievous's people for generations and Grievous is a hero out for revenge. Other than that fact, not much info is known about the Kaleesh Slaughter as George Lucas was very vague on this subject for the The Clone Wars Grievous Hero's backstory. However, the backstory for evil Legends Grievous explained more about the Jedi attack on the Kaleesh.
Due to no known reason why the Jedi slaughtered Grievous's innocent people, some fans speculate the Jedi did it because of fear, as they feared Grievous's Kaleesh people were going to be a threat to them in the future. Fear isn't a justifiable reason to kill a whole species since the species didn't do anything wrong to the Jedi as that could be the reason.
Also in the Canon Ultimate Star Wars reference book, it states that Grievous has a vengeful lust for slaying Jedi, proving once again that the Kaleesh Slaughter happened as there is no Huk and Grievous is a hero out for revenge and it's a fact.