He was the last of the Hapsburg line in Spain and his death without direct issue was signal for the outbreak of the War of the Spanish Succession, where HRE Charles VI sought unsuccessfully to attain the Spanish throne.

Son of Philip I "the handsome" and Juana "the Mad", monarchs of Castile.

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He ruthlessly suppressed the Moors in Spain (1571); Married ¤Mary I of England, but had renounced any claim to the English crown as part of the marriage contract. Upon her death, his suit to her successor, ¤Elizabeth I, was rejected. ¤Mary Queen of Scots had named him heir to her claim to the English throne and, on her death, Philip prepared the "Invincible Armada" for invasion. Defeat of the Armada marked passage of rule of the seas from Spain to England. wiki:

In 1529, his forces successfully repelled Suleiman's assault on his capital at Vienna (First Battle of Vienna).

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Rudolf II was one of the most eccentric European monarchs of that or any other period. Rudolf collected dwarfs and had a regiment of giants in his army. He was surrounded by astrologers, and he was fascinated by games and codes and music. He was typical of the occult-oriented noblemen of this period and epitomized the liberated northern European prince. He was a patron of alchemy and supported the printing of alchemical literature.

Note that this HRE is called Rudolf II as successor of Rudolf I who was German king (1273-1291) but was not emperor. WIKI