Dark horse is a term used to describe a little-known person or thing that emerges to prominence, especially in a competition of some sort or a contestant that seems unlikely to succeed.

The term began as horse racing parlance. A dark horse is a race horse that is not known to gamblers and thus is difficult to place betting odds on.

The earliest-known use of the phrase is in Benjamin Disraeli's novel The Young Duke (1831). Disraeli's protagonist, the Duke of St. James, attends a horse race with a surprise finish: "A dark horse which had never been thought of, and which the careless St. James had never even observed in the list, rushed past the grandstand in sweeping triumph."

The term has been used politically in such countries as Peru, Philippines and United States.

Politically, the term reached America in the nineteenth century when it was first applied to James K. Polk, a relatively unknown Tennessee Democrat who won the Democratic Party's 1844 presidential nomination over a host of better-known candidates. Polk won the nomination on the ninth ballot, and went on to win the presidential election.

Dark Horse may refer to:

Katheryn Elizabeth Hudson (born October 25, 1984), known by her stage name Katy Perry, is an American singer, songwriter and actress. Perry grew up with gospel music, and during her first year of high school she pursued a music career as Katy Hudson, releasing her first studio album called Katy Hudson which failed to chart. She recorded a solo album later, which was never released. After signing with Capitol Music Group in 2007, her fourth record label in seven years, she adopted the stage name Katy Perry.

She first gained recognition with the release of her first mainstream album, One of the Boys in 2008, which spawned three Billboard Hot 100 top-ten songs—"I Kissed A Girl", "Hot n Cold" and "Waking Up In Vegas". Perry supported the album with her Hello Katy Tour. In 2010, her third studio album, Teenage Dream (2010), which topped the Billboard 200 chart, and spawned five number one singles—"California Gurls", "Teenage Dream", "Firework", "E.T." and "Last Friday Night (T.G.I.F.)"—Teenage Dream was the only album (after Michael Jackson's Bad)—to do so, and the first female in history to achieve this milestone. She embarked on the California Dreams Tour, which grossed nearly $60 million worldwide. Perry re-released the album under the name of Teenage Dream: The Complete Confection on March 26, 2012, and the re-release has already spawned the number-one single "Part of Me".

Jordan Houston, better known by his stage name Juicy J (born April 5, 1977) is an Academy Award-winning American rapper and record producer from Memphis, Tennessee and is the co-founder and a member of the duo Three 6 Mafia (formerly known as Triple Six Mafia). He is also the younger brother of fellow member, Project Pat. His second solo album, Hustle Till I Die, was released June 16, 2009. He won an Academy Award for Best Original Song for "It's Hard out Here for a Pimp". In December 2011 Juicy J confirmed rumors that he was the newest member of Wiz Khalifa's "Taylor Gang." He is featured with other members of Taylor Gang on the cover of Source Magazine's May 2012 issue.

Juicy J is most notable for his crunk style of rapping, highlighted by his patented "heavy-breathing" and "stomping" background sound effects. Juicy J's production style is characterized by fast-rolling high hats, sharp snares, and deep cinematic bass. He also incorporates samples from classic soul artists such as Willie Hutch, David Ruffin, and Isaac Hayes.

Christina Victoria Grimmie (born March 12, 1994), known on YouTube as zeldaxlove64, is a pianist and singer/songwriter known for her covers of hit songs by artists such as Demi Lovato, Selena Gomez, Christina Aguilera, Miley Cyrus, Justin Bieber, Katy Perry and many more. In June 2011, she released her debut EP, Find Me.

Christina Grimmie is best known for her cover with fellow Youtuber, Sam Tsui, of Nelly's "Just a Dream" which has had about 60 million views between the two official versions of the video as of May 15, 2012. Her first video was "I Don't Wanna Be Torn", originally by Hannah Montana. She first reached YouTube stardom early on with her cover of Miley Cyrus's "Party in the U.S.A." on August 2009. Since, she's had over 289 million views and over 1.5 million subscribers on her channel as of May 15, 2012, which has made her the 4th most subscribed musician on YouTube. She also placed at number 2 at the top 5 of the MyYoutube competition, behind Selena Gomez, and in front of Rihanna, Nicki Minaj and Justin Bieber.