Apoptotic adaptor molecule that recruits caspase-8 or caspase-10 to the activated Fas (CD95) or TNFR-1 receptors. The resulting aggregate called the death-inducing signaling complex (DISC) performs caspase-8 proteolytic activation. Active caspase-8 initiates the subsequent cascade of caspases mediating apoptosis. Involved in interferon-mediated antiviral immune response, playing a role in the positive regulation of interferon signaling. Can self-associate. Interacts with CFLAR, PEA15 and MBD4. When phosphorylated, part of a complex containing HIPK3 and FAS. May interact with MAVS/IPS1. Interacts with MOCV v-CFLAR protein and PIDD1. Interacts (via death domain) with FAS (via death domain). Interacts with CASP8 (By similarity). Interacts directly (via DED domain) with NOL3 (via CARD domain); inhibits death-inducing signaling complex (DISC) assembly by inhibiting the increase in FAS-FADD binding induced by FAS activation. Interacts with RIPK1, TRADD and CASP8 (By similarity). Component of the AIM2 PANoptosome complex, a multiprotein complex that drives inflammatory cell death (PANoptosis) (By similarity). Interacts with stimulated TNFRSF10B (By similarity). Contains a death domain involved in the binding of the corresponding domain within Fas receptor. The interaction between the FAS and FADD death domains is crucial for the formation of the death-inducing signaling complex (DISC). Phosphorylated.