Cardinal-Infante Ferdinand (also known as Don Fernando de Austria, Cardenal-Infante Fernando de España and as Ferdinand von Österreich; 16 May 1609 – 9 November 1641) was a Spanish and Portuguese prince (Infante of Spain, Infante of Portugal (until 1640)), Governor of the Spanish Netherlands, Cardinal of the Holy Catholic Church, Archduke of Austria, Archbishop of Toledo (1619–1641), and a general during the Thirty Years' War, the Eighty Years' War, and the Franco-Spanish War. He is commonly considered the last great commander and strategist of the Spanish Empire, whose premature death in a critical moment helped bring about the end of Spanish hegemony in Europe.

Born at the El Escorial near Madrid, Spain in 1609, he was the son of the King of Spain and Portugal, Philip III and II and Margaret of Austria, sister of Emperor Ferdinand II. His older siblings were King Philip IV and III and the French queen Anne of Austria.

As his father wished that he pursue an ecclesiastical career, Ferdinand was elevated to the Primacy of Spain in 1619, becoming Archbishop of Toledo. Shortly afterwards he was created Cardinal. The style Cardinal-Infante was a combination of his dignity as Cardinal and his station as a royal Prince (Infante in Spanish) of Spain.

In 1630 the Cardinal Infante's aunt Isabella Clara Eugenia planned to make him her successor as governor of the Spanish Netherlands. To move to the Netherlands in a style befitting a governor, a strong army had to accompany him. Travel by ship from Spain was not an option as it would expose him to risk of battle with the Dutch navy in the then ongoing Eighty Years' War, so in 1633, he went to Genoa, having quit his governorship of Catalonia where he had been trained. He met with an army from Milan for a planned march through the famous Spanish Way across Lombardy, Tyrol, and Swabia, and then following the Rhine to the Netherlands. Ferdinand also planned to secure this supply route with a string of garrisons, and to support the army of King Ferdinand III of Hungary, his brother-in-law the emperor's son and heir, who was leading the Imperial army facing the Swedes in the Thirty Years' War.

Since disease delayed his travels, he sent half of his army ahead under the command of the Duke of Feria. However, this army was severely depleted during fighting with the Swedish army of Bernhard of Saxe-Weimar and Gustaf Horn. The Spanish requested 4000 cavalry from the Imperial general Albrecht von Wallenstein, but this being denied, the Spanish had to fund the troops on their own. The Cardinal-Infante was able to continue his travels in 1634, collecting in Bavaria the remains of the army of Feria, who had died in January 1634.

Meanwhile, Ferdinand of Hungary was able to defeat the Swedish army at Regensburg in July 1634. Ferdinand and his cousin the Cardinal-Infante Ferdinand then raced to merge their armies. The Swedish forces of Bernhard of Saxe-Weimar and Gustaf Horn desperately tried to prevent this merger, but were unable to catch up with Ferdinand of Hungary. The Cardinal-Infante crossed the Danube in August 1634. In September both armies were able to merge, and camped south of Nördlingen in Swabia. At that time Nördlingen was protected by a small Swedish garrison. Shortly thereafter, the armies of Bernhard of Saxe-Weimar and Gustaf Horn also reached Nördlingen, preparing the events for the decisive Battle of Nördlingen. Cardinal-Infante Ferdinand and his cousin Ferdinand then prepared for battle, ignoring the advice of the more experienced generals, such as the Imperial general Matthias Gallas. Bernhard and Horn also prepared for battle, but they were by now rivals and in disagreement with each other. They also underestimated the numerically superior enemy forces, due to incorrect reports that did not realize the Spanish Army of the late Duke of Feria had joined the Cardinal-Infante and believed that the enemy forces numbered only 7,000, not 21,000 infantry, compared to 16,000 Swedish infantry. During the battle, almost anything that could go wrong went wrong for the Swedish forces, in large part due to the efforts of the Spanish Infantry, so that the two Ferdinands achieved a great victory. The Swedish army that fled to Heilbronn was only a shadow of its former self.

The King of Hungary tried to convince his cousin to stay and to strengthen their hold on Germany, but the Cardinal-Infante Ferdinand moved his troops almost immediately after the battle to continue to Brussels. At the end of 1634 he entered Brussels with all the glory befitting a Governor-General. Due to the unpopularity of the clergy in Brussels, he downplayed his religious status and instead emphasized his worldly ranks. Ferdinand was a skilled politician and diplomat, and quickly reformed the government and the military. He especially managed to win the support of the Flemings against France. However, his powers were secretly limited, and the leader of his army was instructed to follow Spanish orders instead of Ferdinand's orders if necessary.

In 1635, the French attacked Namur, planning to merge with the Dutch near Maastricht but were held off by well prepared defenses. At the siege of Leuven, the invading Franco-Dutch forces, suffering badly from supply problems and greatly depleted by disease and desertion, were forced to withdraw when a Spanish relief force arrived. This allowed Spanish forces under Ferdinand to go on the offensive. The Dutch were driven back and the French retreated. Ferdinand subsequently was able to capture Diest, Goch, Gennep, Limbourg, and Schenkenschanz.