Summary: Chyna was one of the most iconic wrestlers of the "Attitude Era"; one of only a few female wrestlers respected enough to be matched up against her male co-workers, and to date, the only female wrestler to have ever held a "serious" title in a mainstream American wrestling promotion (the Intercontinental Championship, second-most prestigious title in the WWE, which she held not once, but TWICE).
Around 2000, at the height of her popularity, Chyna's real-life boyfriend, fellow wrestler Triple H, began to have an on-screen relationship with Stephanie McMahon, daughter of the WWE's owner, Vince McMahon. At the time, the romance between Triple H and Stephanie was played off as merely part of "the storyline", with the two characters they played falling in love, getting "married", and eventually divorcing. Many DDTs and suplexes were had by all! However, not long after beginning the McMahon-Helmsey storyline, Triple H started having *a real-life affair* with Stephanie; an affair which the two of them kept from Chyna for over a year. In 2001, with their onscreen storyline fading, Triple H and Stephanie finally made their real-life relationship public. Chyna was fired soon thereafter.
Triple H, who married Stephanie for real in 2003, is currently one of the most powerful executives in the business; the heir-apparent to Vince's billion-dollar media empire. So given their immense wealth and privilege, what have Triple H and Stephanie decided to do to Chyna, the jilted former lover? Naturally, they've been fucking with her. A LOT.
A full catalogue of all the shit Stephanie, Triple H, and their WWE underlings put Chyna through over the years would require a whole week's worth of videos, but some of the highlights include:
1) withholding royalties from Chyna. Chyna's been pretty hard-up for cash since getting kicked out of the business, and you can see in the third video linked above just how the WWE's legal team treated her.
2) harassing her over her name. Like many former athletes, Chyna tried to move on to the next period of her career after leaving the WWE - making public appearances, doing signings, etc. However, the WWE insisted they held full copyright over the name "Chyna", and forbid her from making any sort of public appearances under that name. This turned into a rather lengthy legal battle, culminating in her decision to *legally* change her name to Chyna. That's why, here in this video, she is very careful to point out that her legal name is Chyna, not Joan - because the WWE, which wouldn't even pay her the royalties she was owed, never stopped fucking with her over a name.
3) the Hall of Fame controversy. This is a really big issue, and probably requires a whole 'nother video to explore fully, but basically Chyna was trying to get into the WWE's Hall of Fame, and was denied - allegedly because she had starred in pornographic material. There are many reasons why this is horseshit - and why Triple H very clearly KNOWS this is horseshit - but it's the only thing he and Stephanie have been able to come up with so far.
tl;dr: Chyna's boyfriend cheats on her and sleeps his way to the top of the industry. He and his hot new billionaire wife get Chyna fired, and proceed to spend the next decade-and-a-half snubbing, slut-shaming, and financially harassing her.
Meanwhile, Chyna stays kind and classy, right up to the end.