Who was the 9th Avatar of Vishnu and what was his story??

As we all know about almost all the Avatars of Lord Vishnu from Matsya(1st) Avatar to Krishna(8th) Avatar and Kalki(10th) Avatar. But there is no clarity about who was the 9th Avatar of Vishnu? Was he Gautama Buddha or any other??? Some say that Buddha was the 9th Avatar not the Gautama Buddha one. What is your take on this???