Sima Yu
Sima Yao was born in 362, when his father Sima Yu was Prince of Kuaiji and prime minister for his grandnephew, Emperor Ai. Sima Yao's mother, Li Lingrong, was originally a servant involved in textile production but, based on a magician's words that she would bear his heir (his sons all having died early by that point), Sima Yu took her as his concubine and she gave birth to Sima Yao. As he was born at dawn, she named him Yao, with the courtesy name Changming, both meaning "dawn". A year later she gave birth to his brother, Sima Daozi. As the oldest surviving son of Sima Yu, Sima Yao was designated as the heir apparent early in his life, and in 365, when he was just three years old, Emperor Fei offered the greater title of Prince of Langya to his father and the title of Prince of Kuaiji to him. Sima Yu declined, both personally and on his son's behalf, and Emperor Fei did not insist on them taking on the greater titles.