Robert Clive Napper was born on February 25, 1966, in Erith, southeast London. He was the eldest child of Brian Napper, who worked as a driving instructor, and his wife, Pauline. Robert grew up in a nearby area called Abbey Wood. His parents had a violent marriage, and he witnessed his father abuse his mother. When Robert was nine years old, his parents divorced. Following the divorce, he and his siblings, which included two brothers and a sister, were placed in foster care. They also went through psychiatric treatment for six years at Maudsley Hospital in Camberwell.

At school, Robert was socially awkward. His classmates did not accept him, and many of them described him as "despised." At the age of 13, he experienced a significant change in his personality. This change followed a camping holiday when a family friend sexually assaulted him. After the assault, Robert became introverted and very neat. His mother noted that he became reclusive. During this time, he also began to bully his siblings and displayed troubling behaviors, including spying on his sister when she was naked.

In 1986, Robert Clive Napper was first known to the police after a conviction involving an airgun. In 1989, his mother reported that he had confessed to a rape on Plumstead Common to the authorities. However, no matching case was found, and the police did not pursue it further.

On July 15, 1992, Napper committed a grave crime on Wimbledon Common. He stabbed Rachel Nickell 49 times in front of her two-year-old son, Alex, who was left crying and pleading for his mother to wake up. Following the incident, police questioned Napper about various unsolved attacks on women, but he was eliminated from their inquiries.

In November 1993, Napper attacked a mother and daughter at their home in Plumstead. He killed 27-year-old Samantha Bisset by stabbing her in the neck and chest. He also assaulted and smothered her four-year-old daughter, Jazmine. Napper later mutilated Samantha’s body and took parts as trophies. The crime scene was so shocking that the police photographer ended up taking two years off due to the trauma.

In May 1994, police arrested Napper after finding his fingerprint at the Bisset home. He was charged with the murders of Samantha and Jazmine. By October 1995, he was convicted at the Old Bailey and acknowledged guilt in two cases of rape and two attempted rapes. Napper has been held in Broadmoor Hospital since his trial.

In December 1995, he was questioned again about the murder of Rachel Nickell but denied being involved. Over the years, Napper has been linked to numerous attacks attributed to the "Green Chain Rapist." This rapist committed at least 70 attacks across southeast London, and some of the earliest cases matched those Napper admitted to.

The investigation into Nickell’s murder initially led detectives to suspect Colin Stagg, an innocent man. However, advancements in DNA profiling in 2004 connected Napper to the crime. On December 18, 2008, he was convicted of manslaughter for Nickell's death, citing diminished responsibility, and he admitted to four additional attacks on women. Following this, he received a sentence of indefinite detention at Broadmoor.