Ferdinand IV, El Emplazado or "the Summoned," (December 6, 1285 – September 7, 1312) was a king of Castile (1295 - 1312). He was a son of Sancho El Bravo and his wife Maria de Molina.

His strange title is given him in the chronicles on the strength of a story that he put two brothers of the name of Carvajal to death tyrannically, and was given a time (plazo) by them in which to answer for his crime in the next world. But the tale is not contemporary, and is an obvious copy of the story told of Jacques de Molay, grand-master of the Temple, and Philippe Le Bel.

His minority was a time of anarchy. He owed his escape from the violence of competitors and nobles, partly to the tact and undaunted bravery of his mother Maria de Molina, and partly to the loyalty of the citizens of Ávila, who gave him refuge within their walls. As a king he proved ungrateful to his mother, and weak as a ruler.

In 1302 he married Constance, daughter of King Denis of Portugal. Their children were:
1. Leonor (1307-1359), married King Alfonso IV of Aragon
2. Constanza (1308-1310)
3. Alfonso XI of Castile (1311-1350)

He captured Gibraltar in 1309, with the help of Aragón. He died suddenly in his tent at Jaén when preparing for a raid into the Moorish territory of Granada, on September 7, 1312.