 Blenheim was a brown horse standing 15.3 hands high with a white star and a white sock on his left hind leg, bred by Henry Herbert, 6th Earl of Carnarvon at his Highclere stud.He was sired by the good sire Blandford, a three-time British champion sire, whose other progeny included Bahram, Brantome, Trigo, Pasch and Windsor Lad.Blenheim's dam, Malva (1919–1941) who stood barely 15 hands, won three minor races for Lord Carnarvon before becoming a highly successful broodmare.