Here are a few contenders, along with why they might be considered the most famous:
* Mr. Ed: This talking horse was a huge television star in the 1960s, and he's still fondly remembered today. His catchphrase "Wilbur!" is iconic.
* Spirit: From the popular animated movie "Spirit: Stallion of the Cimarron," this horse is a symbol of freedom and wildness.
* The Disney Horses: From Cinderella's horses to the many horses featured in classic Disney films, these horses have captured the imaginations of generations.
* My Little Pony: While not a single horse, the My Little Pony franchise features a wide array of colorful and beloved ponies. They are particularly popular with young girls.
Ultimately, the "most famous" cartoon horse depends on individual preferences and experiences. Who's your favorite?