Ramon Berenguer IV, Count of Barcelona the Saint ( b. ca. 1113, d. August 6, 1162) is most known for effecting the union between Catalonia and Aragon.

He inherited the county of Barcelona from his father Ramon Berenguer III on August 19, 1131. On August 11, 1137 in Huesca he was betrothed to the infant Petronila of Aragon, aged 3 at the time. Her father, Ramiro II of Aragon the Monk, who sought Barcelona's aid against Alfonso VII of Castile, abdicated on November 13 that same year, leaving his kingdom to Petronila and her husband. The latter essentially became ruler of Aragon, although he never styled himself king, but instead Count of Barcelona, Prince of the Kingdom of Aragon. He was the last Catalan monarch to use the title of Count as his first; starting with his son Alfonso II of Aragon the counts of Barcelona styled themselves, in the first place, as kings of Aragon.

The treaty between Ramon Berenger and his father-in-law stipulated that their descendants would rule jointly over both realms. Even should Petronila die before the marriage could be consummated, Barcelona would still inherit the Crown of Aragon. Both realms would preserve their laws, institutions and autonomy, remaining legally distinct but federated in a dynastic union under one ruling House.

Historians consider this arrangement the political masterstroke of the Hispanic Middle Ages. Both realms gained greater strength and security and Aragon got its much needed outlet to the sea. On the other hand, formation of a new political entity in the southeast at a time when Portugal seceded from Castile in the west gave more balance to the Christian kingdoms of the peninsula.

Ramon Berenguer successfully pulled Aragon out of its pledged submission to Castile, aided no doubt by the beauty and charm of his sister Berenguela, wife of Alfonso the Emperor, for which she was well-known in her time. After that, in the middle years of his rule, his attention turned to campaigns against the Moors. In 1147 he helped Castile to conquer Almería. In 1148 he turned against the lands of the Almoravid taifa kingdom of Valencia and Murcia, capturing Tortosa and, the next year, Fraga, Lleida and Mequinenza in the confluence of the Segre, Cinca and Ebro. The reconquista of the actual Catalonia was complete.

Ramon Berenger also campaigned in Provence, helping his brother Berenguer Ramon and his infant nephew Ramon Berenguer II against Counts of Toulouse. During the minority of Ramon Berenger II the Count of Barcelona also acted as the regent of Provence (between 1144 and 1157).

In 1151 Ramon Berenguer the Saint founded and endowed the royal monastery of Poblet . He died in 1162 in Borgo Sam Dalmazzo, Piedmont, Italy, leaving his Aragon and Catalonia to his eldest son Ramon Berenguer, who, in compliment to the Aragonese, changed his name to Alfonso and became Alfonso II of Aragon, I of Catalonia. Ramon Berenguer's younger son Pedro inherited the county of Cerdanya and lands north of the Pyrenees.

Ramon Berenguer's marriages and descendants

• First wife, Petronila of Aragon
  • Dolça or Dulce Berenguer (b. 1152, d. 1198) -> married King Sancho I of Portugal the Populator
  • Alfonso II of Aragon (I of Catalonia and Provence) the Chaste or the Trobadour (born Ramon Berenguer, 1157, d. 1196)
  • Pedro, Count of Cerdanya, Carcassonne and Narbonne, (born 1152, d. in the 1160s).
  • Ramon Berenguer III, Count of Provence (born Pedro, 1158, d. 1181)
  • Sancho, Count of Roussillon, Regent of Aragon (b. 1161, d. 1226).

• Unknown mistress
  • Ramon Berenguer, Abbot of Montearagon, Archbishop of Narbonne

Preceded by: Ramon Berenguer III

Count of Barcelona

Succeeded by: Alfonso I