Oligodendrocytes are vital for the functioning of the nervous system. Oligodendrocyte-created myelin sheaths work as dynamic partners which play a substantial role in the myelination of axons. In addition to its well-known functions of providing insulation and enhancing conduction velocity, myelination controls axons' maturity, longevity, and regenerative ability via trophic support and signalling molecules. Myelination also regulates ion concentration and offers neuroprotection. Myelin is generated via complex procedures including cell differentiation, specialised lipids, and protein synthesis. Understanding the physiology of myelin sheath formation is required to understand various neurological disorders associated with myelin sheath damage. This review focuses on our growing understanding of the intricate actions and changes in oligodendrocytes during the course of evolution and in Alzheimer's disease.