Title: Italian War of 1521–1526
Content: quickly proved flawed as the intervention of Henry of Nassau drove back the Meuse offensive; and although de Foix was initially successful in seizing Pamplona, he was driven from Navarre after being defeated at the Battle of Esquiroz on 30 June 1521. Charles was meanwhile preoccupied with the issue of Martin Luther, whom he confronted at the Diet of Worms in March 1521. The Emperor viewed Catholicism as a natural way of binding the diverse principalities of the Holy Roman Empire to him. Since Pope Leo X, for his part, was unwilling to tolerate such open defiance of his own

Title: Schmalkaldic War
Content: authority. At the 1521 Diet of Worms Emperor Charles V had Martin Luther banned and the proliferation of his writings prohibited, which in 1529 provoked the Protestation at Speyer by several Lutheran estates. The tensions culminated to an open conflict over the Lutheran Augsburg Confession of 1530, the Apology of which, written by Philipp Melanchthon, was rejected by the Emperor. In turn several Lutheran states led by Elector John Frederick I of Saxony and Landgrave Philip I of Hesse met at the town of Schmalkalden, where they established the Schmalkaldic League in 1531. In 1544 Charles V returned to Germany

Title: Protestation at Speyer
Content: strife did not figure in his political plans. The Edict of Worms had been suspended in 1526, when the Diet of Speyer decided that every prince should hold whichever religious beliefs he could justify before his King and God. Three years after the Diet of 1526, on the 1 March 1529 Charles V announced the second Diet of Speyer. He again let himself be represented by his brother Ferdinand, as he could not personally appear due to the war with France. In his opening address Ferdinand gave the decision of the Emperor: the annulment of the Diet's decision in 1526,

Title: Charles V, Holy Roman Emperor
Content: positive, but rendered difficult by enormous distances. In effect, however, the Safavids did enter in conflict with the Ottoman Empire in the Ottoman-Safavid War, forcing it to split its military resources. The issue of the Protestant Reformation was first brought to the imperial attention under Charles V. As Holy Roman Emperor, Charles called Martin Luther to the Diet of Worms in 1521, promising him safe conduct if he would appear. Initially dismissing Luther's theses as "an argument between monks", he later outlawed Luther and his followers in that same year but was tied up with other concerns and unable to

Title: Charles V, Holy Roman Emperor
Content: League's troops out of southern Germany, and defeated John Frederick, Elector of Saxony and Philip of Hesse at the Battle of Mühlberg, capturing both. At the Augsburg Interim in 1548, he created a solution giving certain allowances to Protestants until the Council of Trent would restore unity. However, members of both sides resented the Interim and some actively opposed it. In 1552 Protestant princes, in alliance with Henry II of France, rebelled again, which caused Charles to retreat to the Netherlands. During his lifetime, Charles V had several mistresses, but only during his bachelorhood and only once during his widowhood;

Question: Whom did Charles V confront at the Diet of Worms in 1521?
Answer: Marin Luther