The type of monkey that has a red bottom is the mandrill. Mandrills are known for their strikingly colorful faces and distinctive red and blue markings on their faces and rear ends. The red bottom, or rump, is more prominent in males and serves as a visual signal to other mandrills. This coloration is thought to play a role in social interactions and mating displays. Mandrills are native to the rainforests of Central Africa and are the largest species of monkey in the world.