Billy Underwood.
Billy Underwood (born 1983) was the son of Doug and Lisa Underwood and the older brother of Josh Underwood. He was abducted on September 21, 1990 from his school playground as his mother talked with another woman. He disappeared in broad daylight and no progress was ever made in the search for him or his body. In 2000, he miraculously reappeared, albeit without having aged a single day.
The bizarre nature of his reappearance brought in FBI Special Agents Dana Scully and John Doggett to investigate. While Lisa Underwood was thrilled at Billy's return, her husband and second son, Josh, were frightened – particularly when Billy appeared to attack Josh with a bloody hunting knife. As the agents continued their investigation, they learned of the involvement of Ronald Purnell in Billy's disappearance. Purnell had been forced into drugging Billy for abduction by Cal Jeppy. Doggett got Purnell to help and ultimately arrested Jeppy, who had also kidnapped Josh Underwood. On Jeppy's property, the agents discovered Billy's corpse and the boy – which they now understood to be a strikingly realistic apparition, of sorts – disappeared again. (TXF: "Invocation")