Tango was one of two horses owned by Starfleet Captain Christopher Pike at his home in Mojave, the other horse being Mary Lou. Tango was fond of sugar cubes, and Pike often kept a supply in his jacket pocket. Pike often rode out to the park land surrounding Mojave with Tango and a picnic lunch.
In 2254, while attempting to mentally manipulate Pike into accepting an illusionary reality, the Talosians inserted a telepathic scenario into his mind, wherein he found himself back home in Mojave with Tango, as well as a version of Vina, a Human woman they wished Pike to romance. (TOS: "The Cage", "The Menagerie, Part I", "The Menagerie, Part II")