Romulus was the oldest of Ewart's hybrid horse/zebras, born on 12 August 1896. His dam, Mulatto, was an Island of Rum pony lent for Ewart's experiments by Lord Arthur Cecil. In The Penycuik Experiments, Ewart described Romulus as combining 'all the grace and beauty of an antelope and a well-bred Arab foal. Instead of, like his sire, looking as if freshly painted for a Lord Mayor's Show, he was faultless in colouring and in the disposition of the stripes, spots, and bands.'