Harold Shipman: (AKA: Dr.Death ) A married man with a job, might be the last person you would expect to be a murderer, managed to kill over 200 people or possibly even more. He was a popular British physician, who started in 1972, killing 71 patients at his first clinic location and then around twice that amount at his second practice. He murdered a lawyer and tried to fake her will with him a the sole beneficiary. The lawyer (his last victim) had a daughter who was suspicious of the changes and had the police investigate Harold Shipman. Police found clues that pointed to him being the killer of 218 victims, many believe the actual number is quite a bit more. However, with limited evidence, he was only charged for 15 murders. In 2004 he killed himself while serving his prison time, but never actually admitted he killed anyone.
Sources: http://www.history.com/news/history-lists/8-of-historys-most-notorious-serial-killers , https://www.bing.com/images/search?view=detailV2&ccid=uEbfbVlv&id=EE5F0374988BD8FC630235D022AB4EC3478112B2&thid=OIP.uEbfbVlvo3jbUFPMwpjthwDYDY&q=harold+shipman+copyright+free&simid=608045543989972358&selectedIndex=1&ajaxhist=0