The Colonel was the US army colonel who was the primary antagonist of the film.
He was stationed at the US army outpost where Spirit was taken to. The Colonel decided to have the horse tamed, but when he resisted all attempts, he ordered that the horse be tied to a post for three days without food or water in order to weaken him. Around the same time a Lakota Native American named Little Creek was also captured, so the Colonel had him tied up to a post as well. After three days the Colonel had Spirit saddled and appeared to break him in, but the horse regained his second wind and threw him. Seeing the reaction the other horses in the outpost had to this, the Colonel tried to shoot Spirit when Little Creek broke free, stopping the Colonel and escaping with Spirit and the other horses.
The Colonel was next seen when he led his troops to attack Little Creek's village. During the fight, Little Creek charged him, but was stopped when the Colonel shot his horse Rain. He was about to finish the Native American off but Spirit intervened and knocked the Colonel off his horse.
After Little Creek saved Spirit again, the Colonel and his men discovered them and started another chase, this time into a canyon. Spirit then was cornered, and the Colonel thought that he had them. He was amazed when Spirit jumped an impossible jump to freedom, where the Colonel and his men couldn't follow. One of the troops aimed his gun at the two, but the Colonel stopped him, humbly acknowledging Spirit's feat and decided to give up chasing them.