Clifford Olsen (born January 1, 1940) is a Canadian serial killer who claimed the lives of eleven children in the early 1980s.

He was born in Vancouver and despite being raised in a stable home free of abuse (unlike many other serial killers) he soon showed signs of delinquency. He skipped school frequently and was thirteen when he was first arrested for theft. He was known as a bully, a show-off and was rumoured to torture and kill local animals. In adulthood he picked up dozens of convictions for crimes ranging from fraud, armed robbery and firearms offences, and he spent a great deal of time in prison, although he escaped on several occasions.

On November 17, 1980 Olsen abducted 12-year-old Christine Weller in Surrey, British Columbia. She was found on Christmas day, strangled with a belt and stabbed a number of times. On April 16, 1981, Colleen Marian Daignault, aged 13, vanished. It was five months before her body was found. By then, Daryn Todd Johnsrude, 16, had been abducted by Olsen, who smashed the boy's head in with a hammer and tossed him into a ditch.

In May 1981, Olsen got married. Around this time he was accused of molesting a local 5-year-old girl, although he was not charged owing to lack of evidence.

Just four days after his wedding, on May 19, Olsen abducted and murdered 16-year-old Sandra Wolfsteiner. The following month he killed Ada Court, 13.

Olsen claimed six victims in quick succession in the month of July 1981. There was a 9-year-old boy named Simon Partington, abducted and strangled on the 2nd of the month. A week later he raped and strangled Judy Kozma, aged 14. He took her address book and phoned up her friends and family, playing tapes of her screaming down the telephone. Olsen killed Raymond King, 15, on July 23, and just the following day he abducted an 18-year-old German tourist named Sigrun Arnd, whom he raped and battered to death with a hammer. On July 27th he abducted and strangled Terry Carson, 15.

Olsen had now killed ten children. Because the victims were of both sexes, and only three had been found with the other seven tentatively listed as probable runaways, the cases were not initially linked by authorities. By now, however, the police in British Columbia had finally realized they had a serial killer on their hands and a major investigation was soon under way. They were too late to save Louise Chartrand, 17, whom Olsen battered to death on July 30th with a hammer, burying her corpse in a shallow grave.

Because of his lengthy criminal record, forty-one-year-old Clifford Olsen became the prime suspect. He was questioned but there was not enough evidence to hold him at first. However, on August 12, Olsen was arrested for attempting to abduct two girls.

Olsen eventually came up with a controversial deal: he would confess to the eleven murders, and show police where the bodies of those not recovered were buried, and in return he wanted $10,000 paid to his wife for each victim. The authorities were outraged at this suggestion at first, but they really had little evidence to tie Olsen to the killings, and the families of the missing children were desperate to give their loved ones a decent burial. The agreement was made. In January 1982, Olsen pleaded guilty to eleven counts of murder and was given eleven life-sentences. As agreed, $110,000 was paid to his wife.