Lorenz Marie Hackenholt (born 26 June 1914; official death date 31 December 1945) built and operated the gas chamber at the Bełżec extermination camp. In so doing, he personally carried out the murder of hundreds of thousands of people.

Hackenholt was deeply involved in other Holocaust murders, including other Operation Reinhard camps, and in particular, the murder of mental patients and the disabled in Action T4. Hackenholt was a member of the SS with the rank of Hauptscharführer (First Sergeant).

Hackenholt's full name was Laurenzius Marie Hackenholt. He was born on 26 June 1914 in Gelsenkirchen/Ruhr. His father was Theodor Hackenholt and his mother was Elizabeth Wobriezek. He attended the local elementary school until he reached the age of 14. He then became an apprentice bricklayer. After he passed the trade examination he worked on various building sites.

In 1933, Hackenholt volunteered for the SS. After joining the SS he was sent to a training school on 1 January 1934. After that he volunteered for service in the army, where he was assigned to the 12th Engineers' Battalion. After two years military service he was discharged, and then joined the SS Death's Head troops. He was a skilled driver and mechanic and, beginning in March 1938, served at Sachsenhausen concentration camp in the motor pool. He also worked as a guard at Sachsenhausen.