Diederik Maarten Samsom (Dutch pronunciation: [ˈdidəˌrɪk ˈmaːrtən ˈsɑmsɔm] ^ⓘ; born 10 July 1971) is a Dutch environmentalist and retired politician who was the Labour Party (Partij van de Arbeid PvdA) from 2012 to 2016. He was the first leader in the 70-year history of the PvdA to have been voted out of his position by party members. He later served as head of cabinet for First Vice-President of the European Commission Frans Timmermans and his successor Wopke Hoekstra.

Elected to the House of Representatives between 30 January 2003 and 14 December 2016, he was elected PvdA parliamentary leader as well as party leader on 16 March 2012.^[1] He lost the Labour Party leadership election to Lodewijk Asscher in December 2016. Before his election to the House of Representatives he was CEO of a green energy company and a campaigner for Greenpeace Netherlands.

Diederik Maarten Samsom was born on 10 July 1971 in Groningen in the Netherlands. He was raised in Leeuwarden. His father worked as an internist and his mother as a physiotherapist.

Between 1983 and 1989, he attended the Stedelijk Gymnasium (Municipal Gymnasium) in Leeuwarden. There he became interested in physics, and later he went on to study applied physics at Delft University of Technology.^[2] Samsom specialised in nuclear physics and became a level three radiation protection expert. He graduated in May 1997, obtaining a Dutch engineer's degree (Dutch: ingenieur).^[3] He was also on the board of the national students' union LSVb and edited a yearly edition of the Poenboek, a students' guide relating to monetary issues.

Samsom had been involved in environmental issues long before entering politics. Samsom joined environmental organisation Greenpeace Netherlands in September 1995 as a volunteer. He led several campaigns and projects until he resigned in December 2001, after the PvdA offered him a career in politics.^[4] He also worked as the CEO of Echte Energie (Real Energy), a small green energy trading company, from August 2002 until January 2003.

Samsom became a member of the social democratic Labour party while a student in Delft. He left the party but rejoined in February 2001. He stood as a candidate in the 2002 Dutch general election, but was not elected due to the PvdA receiving insufficient votes in the election. The party regained most of its seats in the 2003 election and this time Samsom had a higher position (nine)^[5] on the list of candidates. He was subsequently sworn in as a member of the House of Representatives on 30 January 2003.^[6]

NRC newspaper referred to Samsom as quizking after he won his fifth televised game show.^[25] Particularly notable are his consecutive victories in the 2005 and 2006 National IQ Tests.^[7] According to the test, he has an IQ of 136.^[26] He also won the popular National News Quiz in 2005 and 2006^[27] and in May 2008 he was crowned winner of the Big History Quiz.^[25]

Samsom was raised in a non-religious family and considers himself an atheist. He is a non smoker and observes a vegetarian diet.^{[4][dead link]} He cites swimming and water polo as his favourite sports.^{[4][dead link]} Samsom divorced in 2016 and has two children. His daughter Benthe was born in 2001 and his son Fane was born in 2006. Samsom mentioned them in several political debates and interviews in a for the Netherlands unprecedented and criticized way, including drawing attention to his daughter's disability.^[28] He also involved his private life and family in his 2012 electoral campaign, most notably by featuring his two children in an official party TV advertisement.^[29][30]

Samsom lived on a houseboat in Broek in Waterland with his ex-wife (then girlfriend) and daughter before moving to Leiden, where he still resides as of 2012.^[2][31] In a 2012 interview with Marie Claire, Samsom admitted that before his marriage he had been unfaithful "perhaps once or twice".^{[32][failed verification][33]}