There has been a question that I have been wondering about for a while. Peter先生 has mentioned it often, and ruminated on the origin of a certain Japanese word, and after my Chinese lesson today, I think that I have the answer.
赵高 was a courtier in ancient China. One day, in order to demonstrate his power to the emperor (who he wanted to overthrow) he brought a deer to the imperial court. He told all of the other courtiers that the animal was a horse. 赵高 was such a nefarious bastard that no one was brave enough to contradict him. He was trying to make a point to the emperor, that everyone was so afraid of him that they wouldn't dare contradict him on such a simple issue.
From this story, we get the Chinese idiom "指鹿为马", or "to point at a deer and call it a horse". When someone is deliberately changing or obscuring the facts for to their own ends, they are said to be "pointing at a deer and calling it a horse".
Is this the origin of the Japanese saying "馬鹿"? There can't be many other idioms that involve horses and deer, and although the meaning of 指鹿为马 isn't quite the same as 馬鹿 I think that the Japanese saying has come from the Chinese idiom.