Yves Guérin-Sérac, real name Yves Guillou (alias Jean-Robert de Guernadec, alias Ralf) (born 1926 in Ploubezre) is a French anti-Communist Roman Catholic activist, former officer of the French army and veteran of the First Indochina War (1945–54), the Korean War (1950–53) and the Algerian War of Independence (1955–62).
He was also a member of the elite troop of the 11ème Demi-Brigade Parachutiste du Choc, which worked with the SDECE (French intelligence agency), and a founding member of the Organisation armée secrète (OAS), a French terrorist group based in Spain which fought against Algerian independence in 1961-62.
It was alleged that he was an instigator of the so-called strategy of tension in Italy, and the main organizer of the 1969 Piazza Fontana bombing.