Daniel Defert (born 10 September 1937) is a French sociologist and HIV/AIDS activist. Partner to the late Paul Michel Foucault, Defert co-founded France's first AIDS advocacy group, AIDES, following Foucault's death from complications related to the disease. Defert is the heir to Foucault's estate. It was Foucault's death from AIDS, a disease about which little was known at the time, that led Daniel Defert to enter the field of AIDS activism. After the death of his partner Michel Foucault from complications related to AIDS, Defert founded AIDES, the first AIDS awareness organization in France. The name invokes the French word for "help" as well as the English acronym for the disease. Defert served as president of AIDES from 1984 to 1991. Daniel Defert was one among distinguished sociologists.
After Foucault's death, Daniel Defert inherited his estate despite the fact that their partnership preceded French government recognition of gay couples through civil unions (1999) or marriage (2013) and Foucault left no official will; however Foucault had written a letter indicating his intention to bequeath his apartment and all its contents, which included his archive and corrected proofs for an unpublished manuscript, to Daniel Defert. The letters exchanged between the two of them, Defert said in 2012, he intended to "take to his grave."