VATICAN CITY (AP) — Pope Francis on Saturday chose a bishop who is a trusted theological advisor from his native Argentina for one of the Vatican’s most powerful positions — head of the watchdog office that ensures doctrinal orthodoxy.

Francis named Monsignor Victor Manuel Fernández, the archbishop of La Plata, Argentina, as the prefect, or chief, of the Dicastery for the Doctrine of the Faith.

Fernández has been nicknamed the “pope’s theologian″ since he is widely believed to have helped author some of Francis’ most important documents.

The Dicastery, or department, enforces orthodoxy of church teaching and disciplines theologians deemed to have strayed from Catholic doctrine in their lectures or publications. But it has taken on considerably more importance to rank-and-file faithful as the stain of pedophile priests spread across the globe in recent decades. Among the department’s duties are evaluating and processing sex abuse allegations against clergy.

Fernández is widely believed to have been a key author behind some of Francis’ most consequential documents, notably “God is Love,” a 2016 exhortation that opened the door to letting divorced Catholics who remarry in civil ceremonies to receive Communion.

Catholic teaching holds that marriage is a sacrament, and that remarried Catholics must live together as brother and sister and abstain from sex as a condition for receiving Communion.

Divorced and remarried Catholics who lament being cut off from the Eucharist have long sought the right to receive Communion, but the change would anger conservative hierarchy and rank-and-file faithful if it were to be codified in teaching some day.

Fernández, 60, replaces retiring Cardinal Luis Ladaria, a Jesuit like Francis who took over in 2017 after the pontiff abruptly removed conservative German Cardinal Gerhard Mueller after a single term leading the doctrine department. Mueller was appointed by Pope Benedict XVI, a darling of church conservatives.

The watchdog office’s new chief plans to take up his post in mid-September, the Vatican announcement of his appointment said.

Fernández is a prolific author and biblical expert who has long had the support of Francis, who before becoming pontiff in 2013, was Cardinal Jorge Mario Bergoglio, archbishop of Buenos Aires. Fernández has made clear that the future pope supported his nomination as rector of the Catholic University of Argentina after critics raised concerns about some of his doctrinal positions.

The doctrinal watchdog office has 16th-century roots in a commission established to deal with heresy and schism. Known originally as the Sacred Roman and Universal Inquisition, the body also scrutinized matters of faith and morals.

In a letter to his new appointee that the Vatican made public Saturday, Francis wrote that the office in its current version has as its “central purpose” safeguarding church teachings that springs from faith in order to “give reason for our hope, but not as enemies who point out and condemn.”