Brahms Heelshire is the titular antagonist of The Boy, portrayed by Jett Klyne (young) and James Russell (adult).
He was the son of a wealthy family called the Heelshires, and was also a serial killer.
He was a sociopathic child who was friends with a young girl named Emily Cribbs. When Brahms was 8 years old, he and Emily wandered into the woods by themselves, where it is assumed Brahms killed her by smashing her head in. After which, he started a fire so as to fake his death and avoid punishment, which resulted in his face becoming horribly burned and scarred.
To protect their son, the Heelshires hid Brahms away in the walls of their mansion and had him declared dead, so that no one could find him. Brahms then began wearing a porcelain doll-like mask so as to hide his mutilated face.
His parents, who by then had grown exhausted, and likely aware they could not care for him forever, hired countless nannies throughout his young adulthood in an attempt to find someone to care for him. However, none of the nannies met his standards. Whether they were killed by Brahms or fired by the Heelshires is unknown. Eventually, Greta Evans applied for the job and was hired, as she was much younger than the other nannies and prospects.
His parents apparently left Brahms with a "nanny" as a parting gift, so that they could kill themselves while making sure he was cared for. He occupied himself by stalking Greta, moving the doll (that was supposed to portray him as a child) around the house.