Cholesterol is a sterol lipid essential to all animal cells, serving as a structural component of cell membranes where it modulates fluidity and permeability. It acts as a precursor for bile acids, steroid hormones including cortisol and sex hormones, and vitamin D. Endogenously synthesized primarily in the liver, it is also obtained from dietary animal products. While vital for physiological functions, elevated serum levels contribute to plaque formation in arteries leading to cardiovascular disease. As a hydrophobic molecule with a polar hydroxyl group, it forms lipoproteins for transport in blood. Its rigid ring structure provides stability to membranes without compromising flexibility.