Willem van Eijk was born on August 13, 1941, in a small village called Korteraar in South Holland. At that time, the Netherlands was under German occupation during World War II. Willem grew up in a large working-class family as one of eight children. Having so many siblings was common in those days.

During his childhood, Willem attended elementary school in a nearby town called Ter Aar. He was often bullied and did not fit in with his classmates. The other children called him “Gekke Willempie," which means "crazy little Willem" in Dutch. This name stuck with him and influenced how he later viewed his actions. As a result of being bullied, Willem began to collect strange items, such as dead insects and dried frogs. He did not like studying and refused to put effort into his schoolwork.

As he grew older, Willem gained a bad reputation in his village for being cruel to animals. He would harm animals for fun, including drowning cats and kicking ducks. His brothers described him as "evil personified" when he was just eight years old. Willem had little to no friends and spent most of his time alone. After finishing elementary school, he struggled in high school and turned to petty crimes to support himself.

Willem van Eijk was involved in several murders across many years. His first known victim was Cora Mantel, a 15-year-old girl. He picked her up while she was hitchhiking in 1971. After committing his crime, he disposed of her body in a ditch. Her body was discovered on June 22, 1971.

Later, on August 19, 1974, Aaltje van der Plaat, 43 years old, was murdered. Her body was found in a cornfield with multiple stab wounds. Witnesses placed van Eijk in the area around the time of the murder. He confessed to killing Aaltje as well as Cora after his arrest.

In the 1990s, van Eijk killed more women. In November 1993, he murdered Michelle Fatol, a 23-year-old prostitute, strangling her to death in a ditch. Annelies Reinders, also a prostitute, was found dead on January 21, 1995. Later, on July 17, 2001, the body of Sasja Schenker was discovered in a canal. Her clothes were found nearby, which led to van Eijk being a suspect. He was arrested on November 12, 2001, and eventually confessed to the murders of Michelle, Annelies, and Sasja.

After his initial release from prison in 1990, several other women disappeared or were found dead in the area. Between his release and re-arrest, police suspected him in several other cases, but he was never formally charged for those crimes.

During his trial in 2002, he was found guilty of the murders of the last three victims and sentenced to life in prison. All of his appeals were denied. He died in prison on June 19, 2019.