Red Rum is a British race horse famous for his spectacular win at The Grand National in 1973 and for going on to win this iconic race two more times.
In Life On Mars (Series 1: Episode 4), Sam Tyler chips in to his colleagues' Grand National betting pool. To Gene Hunt, Sam seems suspiciously confident about Red Rum's chances. Sam later explains this away to Gene by saying he "had a hunch".
Although Sam was only four in 1973, it's no surprise that he knows Red Rum, since the horse became the most famous in Britain and continued making public appearances well after he retired.