Within the MCU continuity, Simu Liu’s Shang-Chi is the son of Tony Leung’s Wenwu, a.k.a. the real Mandarin, whose existence was revealed in the Marvel One-Shot All Hail the King following Ben Kingsley’s Trevor Slattery making a mockery of the name in Iron Man 3.
As the leader of the Ten Rings organization, Wenwu raised Shang-Chi to be one of the world’s greatest assassins, but he allowed his son 10 years to live the life of his choosing.
Now Wenwu is demanding that Shang-Chi take his rightful place in the Ten Rings, but he wants nothing to do with his father’s criminal activities, leading to a clash for the ages.