Susan (A Town Called Mercy)

Susan, known to the Preacher as Joshua, was the Preacher's horse in Mercy, Nevada in 1870. According to the Eleventh Doctor, he preferred the name "Susan" and wanted the Preacher to respect his life choices. The Doctor rode Susan to find Kahler-Jex' ship. (TV: A Town Called Mercy)

Personality
Susan seemed to be an ordinary horse, but was actually revealed to be capable of intelligent thought thanks to The Doctor's ability to speak horse.