Clusterin (CLU) is a glycoprotein that exists in various forms in cells, including nuclear, cytoplasmic, and secreted types. The relative molecular weight of CLU varies significantly due to differences in glycosylation and cleavage. Although CLU is commonly present in mammalian tissues and body fluids, its expression levels differ markedly under physiological and pathological conditions. The existence forms and molecular sizes of CLU in cells vary greatly, contributing to its diverse functions. For example, CLU can participate in the occurrence and development of neurological, fibrotic, and metabolic diseases by regulating cell endocytosis, apoptosis, and other processes. This article will review the structural characteristics, basic functions, and potential regulatory mechanisms of CLU protein in physiological and pathological processes.