John Frederick I (German: Johann Friedrich I. von Sachsen, 30 June 1503 – 3 March 1554), called the Magnanimous (der Großmütige), was the Elector of Saxony (1532–1547) until he was deprived of this title in the Capitulation of Wittenberg by Charles V, Holy Roman Emperor.

At the Elector's Schloss Hartenfels at Torgau, he constructed a chapel specifically designed to be a Lutheran place of worship and invited Martin Luther to deliver the inaugural sermon.

in the translation by Veit Warbeck of the French romance the Magelone, made in preparation of John Frederick's marriage in 1527; Catholic elements are suppressed.

He took an active part in the disturbances caused by the Pack affair (see John the Steadfast), and Luther was grateful to him for his exertions, in spite of his youth, for the maintenance of peace.

The intrigues of Archduke Ferdinand induced him after the diet to draw up an imperial statute for the Evangelical estates, which shows that he was more decidedly convinced of the right and duty of defense than his father.

He followed the efforts at agreement at the conference of Regensburg in 1541 with suspicion and refused to accept the article on justification which had been drawn up under the supervision of Gasparo Contarini to suit both parties, and Luther, his steady adviser, confirmed him in his aversion.

The efforts at agreement failed, and the elector contributed not a little to broaden the gulf by his interference in the ecclesiastical affairs of Halle and by aiding the Reformation which had been introduced there by Justus Jonas.

When the Schmalkaldic War broke out in 1546, he marched to the south at the head of his troops, but the unexpected invasion of his country by his cousin Duke Maurice compelled him to return.

He firmly refused to bind himself to comply in matters of religion with the decisions of a future council or diet, declaring that he was resolved to adhere until his grave to the doctrine contained in the Augsburg Confession.

He met his family after an absence of five years at Wolfersdorf Castle which he had built as a hunting lodge earlier, and he renamed it Schloss Froehliche Wiederkunft ("Palace of Happy Returning").