Quentin Sainz was the CEO of Sainz Pharmaceuticals, a drug company that manufactured an array of pharmaceutical products as well Amylinx, a controversial drug that help ALS, a disease Quentin himself was diagnosed with.. He was in a relationship with Lisa Parker, a contractor at his firm, as was also was the ex-husband of Jessica Pearson.
In the episode "Dirty Little Secrets" Sainz Pharmaceuticals is accused of defrauding the FDA by falsifying clinical trails to get Amylinx on the market. After it was discovered in court that sales jumped to 38 million dollars per quarter just after the company was on the verge of becoming bankrupt, the judge ruled that the case would proceed.
Quentin denied any allegations that he falsified clinical trails, but Harvey was not convinced. It was later discovered that Lisa Parker was the one behind the allegations, she admitted that she took the people who showed signs of liver damage out of the study because it would jeopardize FDA approval. She wanted to do this to try to save Quentin's life, because he also had ALS.
In the episode "Yesterday's Gone"; Jessica reveals to Harvey that Quentin succumbed to the disease and that he named them co-executors of his will.