Specifically, the most likely ancestor of the domestic horse is the Przewalski's horse, a critically endangered wild horse species that still exists today in Mongolia and parts of China.
However, it's important to note that the exact origin of the domestic horse is still debated by scientists. Some researchers believe that domestication may have occurred independently in different regions, with multiple wild horse lineages contributing to the modern domestic horse.
Regardless of the specific origin, the process of domestication is thought to have begun around 5,500 years ago, with horses gradually being brought under human control for various purposes, including transportation, agriculture, and warfare.