Macaca mulatta, commonly known as the rhesus macaque, is a species of monkey native to South Asia. They are characterized by their brown or gray fur, long tails, and expressive faces. Rhesus macaques are highly adaptable and can thrive in various habitats, including forests, grasslands, and urban areas. These primates are known for their social behavior, living in troops that can consist of several dozen individuals. They are also significant in scientific research, particularly in the fields of psychology and medicine, due to their genetic similarities to humans and their role in studies related to vaccines and disease.