Sui-San is an Eternal who was part of a group of Eternals exiled from Earth. They resided on the moon Titan. War broke out among them and Sui-San was the only survivor. When Mentor came to the moon, he and Sui-San wed and turned Titan into what it is today.
They had two sons together, Eros and Thanos. Thanos was born with a different appearance than the rest of their race, and although he was never ridiculed or mistreated, he always felt different. This led him to become mad and obsessed with death.
Thanos caused a nuclear disaster, and while the Titans fought the flames, he kidnapped Sui-San. He then brutally dissected and killed her. She was laid to rest in a tomb deep beneath Titan, where Mentor visits her regularly.
Major Story Arcs
Deadpool Vs Thanos
For more information see: Deadpool vs Thanos
When Deadpool, Thanos, and Black Talon go to Hell looking for Death who they believe has been kidnapped by Mephisto they come across an army of dead. On of the dead is Sui-San and she attacks her son Thanos. It looks like Thanos maybe is trouble but Deadpool decapitates Sui-San, but because Death is gone and she is already dead it is assumed Sui-San is still in Hell fighting for a Hell Lord.