Olav Engelbrektsson (c. 1480, Trondenes, Norway – 7 February 1538, Lier, Duchy of Brabant, Habsburg Netherlands) was the 28th Archbishop of Norway from 1523 to 1537, the Regent of Norway from 1533 to 1537, a member and later president of the Riksråd (Council of the Realm), and a member of the Norwegian nobility. He was the last Roman Catholic to be the Archbishop of Norway before he fled to exile in 1537.

After his death, Olav Engelbrektsson was given a "bad reputation as an untrustworthy and scheming prelate" (dårlig ettermæle som en upålitelig og intrigant prelat) by the Protestant historians. His reputation did not improve after 1814, when Norway made its declaration of independence from Denmark, because he was still blamed for promoting the Catholic Church at the expense of Norwegian independence. But the later historians—Absalon Taranger in 1917, Sverre Steen in 1935 and Lars Hamre in 1998—have rehabilitated most of his reputation with detailed studies and labeled most of the accusations as unfair.

Olav Engelbrektsson is believed to have been born at Trondenes near Harstad in Troms around 1480 as the son of Engelbrekt Gunnarsson and Jorunn. Engelbrekt Gunnarson was a bondefører (a leader of farmers) and storbonde (a large landowner) in Romerike in Eastern Norway around 1447. He kept getting in arguments and fights with the Danish bailiff Lasse Skjold and eventually killed him. Researchers believe that that is why Engelbrekt and Jorunn moved to Trondenes, where his son Aslak was already living because, at that time, Aslak was the wealthiest man between Bergen and Senja. Young Olav was raised in a home that was always opposing the Danish overseers, and that might have been one of the several influences of his attitude towards the Danes in his years as the archbishop.

Olav Engelbrektsson was from an old landowning family in Romerike, and it is often claimed that he and his family belonged to the gentry. King Christian I of Denmark was supposed to have ennobled Engelbrekt Gunnarson and his descendants sometime before 1480 but, in 1961, cand. philol. Trygve Lysaker wrote that the documentation did not exist to such a claim. Nevertheless, the family had a coat of arms—a blue shield showing a red rose surrounded by three lilies.

Five of Olav's relatives belonged to the clergy. Two of them were his paternal uncles Sakse Gunnarsson and Gunnar Gunnarson. Gunnar was a canon in Oslo, a profession that even some of his own sons chose. It is known that Olav and four of these relatives studied at foreign universities. His uncle Sakse was the one who gave Olav clerical education.

There is a prevailing theory among the Norwegian genealogists that Olav Engelbrektsson was not the first member of his family to be the Archbishop of Nidaros. But, throughout his life, the records were more concerned with the church, the politics and the wars than with the families. So there may not be enough evidence to prove that Olav was the grandnephew of the 25th Archbishop Olav Trondsson, the nephew of the 26th Archbishop Gaute Ivarsson and the uncle of his own successor, Torbjørn Olavssøn Bratt, the first Lutheran "superintendent" of Trondheim. He did help with the education and careers of Torbjørn and his brother, Jens Olavssøn Bratt, but their biographies at Norsk Biografisk Leksikon do not name him as their uncle. It is the same with the possibility that Olav's mother might be the daughter of Ivar Trondsson from the Aspa family in Frei in Nordmøre.

Olav Engelbrektsson was enrolled in 1503 at the University of Rostock in Germany, which at that time had between 400 and 500 students. He was already ordained as a priest but he wanted to continue his studies. He eventually took examinations to earn several more degrees at the university—a baccalaureus in 1505 and a Magister's degree in 1507. At the university, theology was being taught by conservatives from the Catholic Church but the city of Rostock was once the center of North German humanism. There were several reformists who came to the university as guest speakers over the years but, when Olav was a student there, the regular teaching was left to the conservatives because the department of theology was led by a deputy commissioner of the business of papal indulgences of the city.

Olav Engelbrektsson soon became the leader of the Norwegian Collegiate Club, called Regentia Sancti Olavi (Senate of St. Olav) in the memory of the martyred King of Norway, Olav the Holy. They were located in a separate building under the Norwegian name of St. Olavs hus (House of St. Olav). Among the students, Engelbrektsson was known as a very sociable person, but not particularly charismatic, and he was not the one who usually followed the ways and beliefs of the club. He became acquainted with, among others, the brothers from Sweden, Johannes Magnus and Olaus Magnus. The brothers would be the last two Catholics to be the Archbishop of Uppsala, but Olaus is still famous for his map of Scandinavia, the Carta Marina of 1537. Engelbrektsson were especially good friends with another Swede, Laurentius Andreae, the archdeacon of Uppsala who quickly became one of the leaders of the Protestant Reformation of Sweden under Gustavus Vasa. By 1515, Olav Engelbrektsson had been at the university for eleven years and had even taught for his own studies, including a brief period at the Catholic University of Louvain. But in 1515 he decided that it was the time to return to his homeland.