Albertus Magnus OP (c. 1200 – 15 November 1280), also known as Saint Albert the Great, Albert of Swabia, Albert von Bollstadt, or Albert of Cologne, was a German Dominican friar, philosopher, scientist, and bishop. He is considered one of the greatest medieval philosophers and thinkers.

Canonized in 1931, he was known during his lifetime as Doctor universalis and Doctor expertus; late in his life the sobriquet Magnus was appended to his name. Scholars such as James A. Weisheipl and Joachim R. Söder have referred to him as the greatest German philosopher and theologian of the Middle Ages. The Catholic Church distinguishes him as one of the Doctors of the Church.

It seems likely that Albertus Magnus was born sometime before 1200, given well-attested evidence that he was aged over 80 on his death in 1280. Two later sources say that Albert was about 87 on his death, which has led 1193 to be commonly given as the date of Albert's birth, but this information does not have enough evidence to be confirmed. Albert was probably born in Lauingen (now in Bavaria), since he called himself 'Albert of Lauingen', but this might simply be a family name. Most probably his family was of ministerial class; his familial connection with (being son of the count) the Bollstädt noble family is almost certainly mere conjecture by 15th-century hagiographers.

Albert was probably educated principally at the University of Padua, where he received instruction in Aristotle's writings. A late account by Rudolph de Novamagia refers to Albertus' encounter with the Blessed Virgin Mary, who convinced him to enter Holy Orders. In 1223 (or 1229), he became a member of the Dominican Order, and studied theology at Bologna and elsewhere. Selected to fill the position of lecturer at Cologne, Germany, where the Dominicans had a house, he taught for several years there, as well as in Regensburg, Freiburg, Strasbourg, and Hildesheim. During his first tenure as lecturer at Cologne, Albert wrote his Summa de bono after having a discussion with Philip the Chancellor concerning the transcendental properties of being. In 1245, Albert became master of theology under Guerric of Saint-Quentin, the first German Dominican to achieve this distinction. Following this turn of events, Albert was able to teach theology at the University of Paris as a full-time professor, holding the seat of the Chair of Theology at the College of St. James. During this time Thomas Aquinas began to study under Albertus.

Albert was the first to comment on virtually all of the writings of Aristotle, thus making them accessible to wider academic debate. The study of Aristotle brought him to study and comment on the teachings of Muslim academics, notably Avicenna and Averroes, and this would bring him into the heart of academic debate.

In 1254, Albert was made provincial of the Dominican Order and fulfilled the duties of the office with great care and efficiency. During his tenure, he publicly defended the Dominicans against attacks by the secular faculty of the University of Paris, commented on John the Evangelist, and answered what he perceived as errors of the Islamic philosopher Averroes.

In 1259, Albert took part in the General Chapter of the Dominicans at Valenciennes together with Thomas Aquinas, masters Bonushomo Britto, Florentius, and Peter (later Pope Innocent V), establishing a ratio studiorum or program of studies for the Dominicans that featured the study of philosophy as an innovation for those not sufficiently trained to study theology. This innovation initiated the tradition of Dominican scholastic philosophy put into practice, for example, in 1265 at the Order's studium provinciale at the convent of Santa Sabina in Rome, out of which would develop the Pontifical University of Saint Thomas Aquinas, the "Angelicum".

In 1260, Pope Alexander IV made him bishop of Regensburg, an office from which he resigned after three years. During the exercise of his duties he enhanced his reputation for humility by refusing to ride a horse, in accord with the dictates of the Order, instead traversing his huge diocese on foot. In 1263, Pope Urban IV relieved him of the duties of bishop and asked him to preach the Eighth Crusade in German-speaking countries. After this, he was especially known for acting as a mediator between conflicting parties. In Cologne, he is known not only for being the founder of Germany's oldest university there, but also for "the big verdict" (der Große Schied) of 1258, which brought an end to the conflict between the citizens of Cologne and the archbishop. Among the last of his labors was the defense of the orthodoxy of his former pupil, Thomas Aquinas, whose death in 1274 grieved Albert (the story that he travelled to Paris in person to defend the teachings of Aquinas can not be confirmed).