Son of King Alfonso VIII of Castile and Eleanor Plantagenet. Paternal grandson of King Sancho III of Castile and Blanca Ramírez of Navarre. Maternal grandson of King Henry II of England and Eleanor, Duchess of Aquitaine.
Enrique became heir to the throne when his older brother died in 1211. He was ten years old when he became King, under the regency of his elder sister Berenguela.
In 1215, he married Infanta Mafalda, daughter of King Sancho I of Portugal. He was only eleven years old when the marriage took place, and his bride was eighteen. Because of his young age, the marriage was not consummated and was annulled in 1216.
Enrique was then betrothed to Infanta Sancha of León, eldest daughter of King Alfonso IX, his eldest sister's former husband. However, the marriage never took place because the King of Castile was unexpectedly killed by a falling roof tile.
He was succeeded by his eldest sister, Berenguela, who abdicated in favor of her son, Ferdinand III.