Pepin the Younger (714-768) was the first King of the Franks of the Carolingian dynasty. In 741 he and his brother Carloman succeeded their father, Charles Martel, as mayors of the palace and de facto rulers of the kingdom during an interregnum (737-743). After the retirement of Carloman (747), Pepin obtained the permission of Pope Zachary to depose the last of the Merovingian kings, Childeric III, and assume the throne. He continued to build up the heavy cavalry which his father had begun. He maintained a standing army to protect the realm and form the core of its full army in wartime. He not only contained the Iberian Muslims as his father had, but drove them out of the country. He continued his father's expansion of the Frankish church and the institutional infrastructure of feudalism that would prove the backbone of medieval Europe. While not known as a great general, he was undefeated during his lifetime. Pepin died during a campaign, in 768 at the age of 54.