Jack Hyde is the main antagonist of the novels Fifty Shades Darker and Fifty Shades Freed (the two sequels to Fifty Shades of Grey) and also the arch-enemy of Christian Grey. Essentially, he is the main antagonist of the trilogy as a whole.
He is set to be portrayed by Eric Johnson in the film adaptations of said novels.
Jack Hyde grew up in a foster home after his parents died. At some point, he met Christian Grey, who was placed in the same foster home. However, when Christian was adopted by the wealthy Grey family, Jack grew to resent them (Christian in particular).
Fifty Shades Darker
Jack Hyde first appears in Fifty Shades Darker as an editor for a publishing company called Seattle Independent Publishing (SIP). He interviews Anastasia Steele (the protagonist) and hires her as his personal assistant. He then starts behaving quite inappropriately towards her, such as constantly asking her out and calling her pet names (to be fair, she was rather unnerved by him to begin with). Eventually, Jack confronts Ana with her personal e-mails to Christian and forces her to have sex with him under threat of exposure. However, Ana is able to escape his clutches, and Christian (who had acquired SIP) has him fired. This causes Jack's resentment to grow enough to seek revenge on Christian. Christian soon discovers that Jack had been spying on him the entire time. Jack is spying on Christian's birthday party, and judging by Elena Lincoln's departure, he may have had a role in sabotaging the party.
Fifty Shades Freed
Jack returns in Fifty Shades Freed.
To enact his revenge against Christian, Jack poses as a worker for a moving company and breaks into Christian's apartment. However, Christian's security team has him arrested and sent to jail, but not before he tries to claim that Ana sexually harassed him (which, of course, isn't true). He is later bailed out by Mr. Lincoln (Elena's ex-husband), who had secretly paid his bail out of spite towards Christian for his affair with Elena. After his release, Jack makes his move by kidnapping Mia (Christian's sister) for a $5 million ransom with the help of his former associate Elizabeth Morgan (whom he blackmailed). Ana rescues Mia, thereby foiling his plan.
Jack is a very sleazy man, constantly blackmailing women by recording them while having sex with them. He also has a single-minded hatred towards Christian, believing that Christian took his life away from him, and went out of his way to get revenge.