Phospho-RIPK1 (Ser166) is a phosphorylated form of Receptor-Interacting Serine/Threonine-Protein Kinase 1 (RIPK1), a key regulator of TNF-mediated apoptosis, necroptosis, and inflammatory pathways. This protein consists of an N-terminal kinase domain, an intermediate domain containing the RIP homotypic interaction motif (RHIM), and a C-terminal death domain. When phosphorylated at Ser166, RIPK1 is involved in the formation of necrosis-inducing complexes and is considered a biomarker for the activation of RIPK1 kinase and necroptosis. This phosphorylation can be effectively inhibited by Nec-1, a necroptosis inhibitor.