The past history of Thanos of Earth-9997 mirrors that of his Earth-616 counterpart. However, at least on Earth-9997 it was revealed that Sui-San was really a Skrull, and had to hide her physiology when Thanos was born. Thanos accidentally stumbled upon the truth, but kept it a secret between the two of them. The fact that the people of Titan persecuted his mother for her appearance fed his hatred towards them all. Apparently Thanos wasn't aware that his mother was a victim of his first strike against Titan, and that Death took on the appearance of his mother to manipulate him for her own ends.
In recent history, Thanos was deceased but his ultimate demise is yet to be revealed, however since his death, Thanos was ever at Death's side, and rallied an army of undead soldiers to counter Mar-Vell's army of heroes hoping to destroy Death and create a paradise in the Realm of the Dead. When Thanos tried to stop Mar-Vell from destroying Death with the Ultimate Nullifier, Mar-Vell used his powers to reveal the truth to Thanos. In a rage, Thanos took the Ultimate Nullifier on Death himself, ignoring her plea to wait.
Realizing his grave error in killing Death, making it impossible for those in the land of the living to move on, Thanos retreated back into the Realm of the Dead and took on the guise of a sign-carrying protester in a part of the Realm which resembled depression-era New York. Thanos attempted to teach Captain America the follies of convincing everyone to go to Paradise.
He eventually aided Captain America, Comet Man (and his son Benny), and 4-D Man in staging a revolt against Mar-Vell in Paradise. Thanos aided in stopping the Kree invasion of Paradise, which was won by the heroes that lived there. Following the defeat of the Kree invaders, Mar-Vell leaving Paradise and instilling Reed Richards with his powers, the ultimate fate of Thanos is unrevealed.