Kartikay was Ganesh's brother. He has his own amazingly psychedelic story - for example when he was born, six different goddesses were so enamored by him that each wanted to nurse him. In response, Kartikay grew six heads. Naturally. He was also the scientist of the Gods (similar in some ways Hephestus), a brilliant general, and a slayer of demons. While Kartikay embodies all the ideas of science, reason, and pure logic, Ganesh symbolizes spiritualism and wisdom. It's no coincidence that they both sprang from Shiva - the model of asceticism, introspection and withdrawl from the world.
Getting back to the story: one day Kartikay and Ganesh decide they're going to race around the whole universe 'cause, you know, why not? Kartikay, full of reason and purpose mounts up his magic peacock and starts the race. Meanwhile, Ganesha walks in a circle around Shiva and Parvati, declaring that the whole universe is really just these two. Everyone applauds and Ganesh wins.
Now, the real question is: why did Ganesh win?
check out Kartikay cruising around on his serpent-eatin' peacock rocket in the background there!