Alexander the Great had two different-colored eyes.
This condition, known as heterochromia iridum, is caused by either an excess or shortage of pigment in one of an individual’s irises. It is also possible to have part of one iris be a different color than its remainder. In addition to Alexander, several modern hotties have this condition, including actors Wentworth Miller, Henry Cavill (the new Superman), Kate Bosworth, and Mila Kunis!
Heterochromia is actually quite uncommon in humans, but can be observed often in other species. Among dogs, this condition is most often observed in the Siberian Husky, Australian Shepherd, and Catahoula Leopard Dog. With cats, “odd eyes” are most commmon within breeds such as the Turkish Van, Turkish Angora, Sphynx, and Japanese Bobtail. In fact heterochromic cats were so prized in Turkey that in 1917 the Turkish government began a program designed specifically to breed odd-eyed cats!