Riek Machar Teny Dhurgon (born 26 November 1952) is a South Sudanese politician who has served as the vice president of South Sudan on several occasions, most recently as the first vice president, since 2020.

A member of the Nuer ethnic group, Machar earned degrees in engineering from Khartoum University and the University of Bradford. In 1984, he joined the Sudanese People's Liberation Army/Movement (SPLM/A) rebel group fighting for southern independence during the Second Sudanese Civil War.

Due to a rift with SPLM/A leader John Garang, Machar was ejected from the group in 1991, and founded the SPLA-Nasir splinter group. Later that year, Machar was involved in the Bor Massacre, in which his forces took part in the massacre of at least 2,000 Dinka civilians. Over the next several years, Machar led several different rebel groups and militias, including the SPLA-United, the South Sudan Independence Movement/Army (SSIM/A), the South Sudan Defence Forces (SSDF) and the Sudan People's Defense Forces/Democratic Front (SPDF), before reuniting with Garang and the SPLM/A in 2002.

Following the end of the Second Sudanese Civil War in 2005, Machar was made Vice President of the Southern Sudan Autonomous Region with Garang's successor Salva Kiir Mayardit as President. Following the South's gaining of independence in 2011, Machar became Vice President of the independent republic of South Sudan with Kiir as President.