Beautiful old style Quarter Horse, the bulldog look from the that look! Nowadays, there's so much Thoroughbred in them, they too long and tall for my taste.>> I disagree and I don't think that's natural.
The American Quarter Horse was one of the first horse breeds native to the United States. (It and the Narragansett Pacer appeared about the same time). The breed evolved when the bloodlines of horses brought to the New World were mixed.