There is no single animal that matches the description of the unicorn as a horse with a horn growing from its forehead. Legends about such animals are based on several different types of animals, including rhinos, narwhals and antelope.
The rhinoceros is a major source for many legends about unicorns. Its horn was often believed to have magical powers, including the ability to cure diseases and neutralize poisons. The horns of narwhals were seen as having similar powers and were highly valued in Medieval Europe. The oryx and the eland are two species of antelope that also contributed to the development of these legends.