After his retirement from racing he became a highly successful breeding stallion: through his grandson Native Dancer he appears in the pedigrees of most modern Thoroughbreds.
Unbreakable was a black horse bred in the United States by his owner, Joseph E. Widener.
The colt was sired by the British-bred stallion Sickle out of the French mare Blue Glass,[1] making him a half-brother to the Belmont Stakes winner Hurryoff.
[3] In the following year he competed at the highest level, finishing fifth to Pasch in the 2000 Guineas and eighth behind Bois Roussel in The Derby.
Unbreakable is inbred 4 × 4 to Sainfoin and St. Simon, meaning those stallions appear twice in the fourth generation of his pedigree.