Joachim I Nestor Hohenzollern (21 February 1484 - 11 July 1535) was an elector of Brandenburg, acceded 1499.

Eldest son of John or Johann Cicero, he received an excellent education, became [[elector of Brandenburg] on his father's death in January 1499, and soon afterwards married Elizabeth Oldenburg , daughter of John of Denmark.

He took some part in the political complications of the Scandinavian kingdoms, but the early years of his reign were mainly spent in the administration of his electorate, where by stern and cruel measures he succeeded in restoring some degree of order . He also improved the administration of justice, aided the development of commerce, and was a friend to the towns. On the approach of the imperial election of 1519, Joachim's vote was eagerly solicited by the partisans of Francis I, king of France, and by those of Charles, afterwards the emperor Charles V. Having treated with, and received lavish promises from, both parties, he appears to have hoped for the dignity for himself; but when the election came he turned to the winning side and voted for Charles. In spite of this step, however, the relations between the emperor and the elector were not friendly, and during the next few years Joachim was frequently in communication with the enemies of Charles.

Joachim is best known as a pugnacious adherent of Catholic orthodoxy. He was one of the princes who urged upon the emperor the necessity of enforcing the Edict of Worms, and at several diets was prominent among the enemies of the Reformers. He was among those who met at Dessau in July 1525, and was a member of the league established at Halle in November 1533. But his wife adopted the reformed faith, and in 1528 fled for safety to Saxony; and he had the mortification of seeing these doctrines also favored by other members of his family. Joachim, who was a patron of learning, established the university of Frankfort-on-the-Oder in 1506. He died at Stendal in 1535.

See T. von Buttlar , Der Kampf Joachims I. van Brandenburg gegen den Adel (1889); J. G. Droysen, Geschichte ier Preussischen Politik (1855-1886).