Acyl-coenzyme A:cholesterol acyltransferase (ACACT; EC 2.3.1.26) is an intracellular protein located in the endoplasmic reticulum that forms cholesterol esters from cholesterol. Accumulation of cholesterol esters as cytoplasmic lipid droplets within macrophages and smooth muscle cells is a characteristic feature of the early stages of atherosclerotic plaques (Cadigan et al., 1988 [PubMed 3335499]).