The Founding Races were the four races which were primarily responsible for the foundation of civilization in the Malazan World before the human race came to dominance. These were K'Chain Che'Malle, Forkrul Assail, Jaghut and Imass.
Other races did exist but they were few and far between, playing little or no part in shaping the world's history It should be noted that this view about the founding races was based on a fragment of a translator's note to a lost edition of Gothos' Folly and as such the information must be viewed as likely being incomplete and possibly not entirely correct. It is also contradicted by T'riss, who described it as "...a self-justifying myth. Just like all of your origin myths."
The K'Chain Che'Malle were the most ancient of the four races, living at least 500,000 years before the start of the Malazan series. They employed the sorcery of Kaschan, manipulating gravity and other forces of the physical world to create enormous artifacts and buildings, such as Skykeeps. They did not worship as such, but this feeling weakened in favor of Eleint.
The Forkrul Assail existed about the same time as the Che'Malle. They employed the sorcery of Ahkrast Korvalain which gave their voices great magical power. They fought wars of eradication against many races, including the Tiste and the Che'Malle.
The Forkrul Assail civilization waned after they lost their war of eradication against the Che'Malle, when their god was shattered and the gate to Ahkrast Korvalain was lost.
The Jaghut dominated the world after the destruction of the K'Chain Che'Malle civilization. They wielded the sorcery of Omtose Phellack. Like the Assail, they were extremely long-lived, essentially immortal unless killed.
They were pacifists for the most part, aside from the Jaghut Tyrants. Suffering great tyranny at the hands of the K'Chain and forseeing their own future, they abandoned civilization to lead solitary lives. Due to the actions of the Tyrants, they would be nearly eradicated at the hands of the T'lan Imass.
Realizing that many of their gods were in truth Jaghut Tyrants and enraged at the indifference of the Jaghut, they conducted a genocide against the Jaghut. Being pacifists, the Jaghut raised huge glaciers in defense, which the mortal Imass could not cross. The Imass undertook the Ritual of Tellann, becoming undead T'lan Imass to continue their war.
The Imass who did not participate in the Ritual would go on to become the ancestors of the Human race.