 Relko was one of three outstanding colts produced by the broodmare Relance, the others being Match II and Reliance (Prix du Jockey Club).He was sired by the Grand Prix de Saint-Cloud winner Tanerko, a representative of the Teddy sire line.Relko was trained by Chantilly by Francois Mathet, who had previously handled the 1955 Derby winner Phil Drake.