Leontes was born in 2013. He is by King Kamehameha out of Cesario by Special Week.
Leontes was awarded Best Two-Year-Old Colt in Japan in 2015. Leontes, out of Japanese Oaks winner Cesario and a half-brother to Japan Cup winner Epiphaneia and Satsuki Sho (Japanese 2000 Guineas) winner Saturnalia, unleashed a powerful late run to win the Grade 1 Asahi Hai Futurity Stakes in only his second career start and became the first horse in the history of the race to accomplish the feat.
Leontes entered stud in Japan in 2017. In 2024, T O Royal earned his first Grade 1 victory in the Tenno Sho (spring). He also won the Grade 2 Hanshin Daishoten and the Grade 3 Diamond Stakes in the same year. In 2025, Museum Mile captured the Grade 1 Satsuki Sho (Japanese 2000 Guineas), setting a race record time of 1:57.0 for 2000 meters on turf at Nakayama while defeating Croix du Nord, who went on to win the Grade 1 Tokyo Yushun (Japanese Derby) in his next start. He later added another top-level triumph by winning the Grade 1 Arima Kinen (Grand Prix)and was awarded Best Three-Year-Old Colt in Japan.
Among his other best progeny are Industria, who took the Grade 3 Lord Derby Challenge Trophy; Buena Onda, who won the Grade 3 Kyoto Kimpai; and Justin Rock, who took the Grade 3 Kyoto Nisai Stakes.