a candidate that the delegates don't know enough about to dislike him
an entertaining simplistic love story centering on
an unknown contestant or one who unexpectedly wins a race
a person who suddenly and unexpectedly receives political support to run for office
a winning tale of the bittersweet glories of life and the transformative power of love
An underrated that wins or has good prospects of winning.
Probably a good horse, but its full potential is unknown.
A dark horse candidate is one who is nominated unexpectedly, without previously having been discussed or considered as a likely choice. Often a dark horse is selected as a compromise when other, more prominent candidates' factions cannot come to an agreement. This metaphoric expression originally alluded to an unknown horse winning a race and was so used in a novel by Benjamin Disraeli (The Young Duke, 1831).
Dark Horse is an album by George Harrison, released as the follow-up to Living in the Material World in 1974. Dark Horse is notable for the well-attended, but ultimately infamous North American tour that supported it, which would turn out to be Harrison's only set of performances there as a solo artist.
The Dark Horse Nebula or Great Dark Horse is a large dark nebula, which as seen from Earth, obscures part of the upper central bulge of the Milky Way. The Dark Horse lies in the southern constellation Ophiuchus (the Serpent Bearer), near its borders with the more famous constellations Scorpius and Sagittarius.
"Dark Horse" is the title track to George Harrison's 1974 album, and later the name of his record label.