|Hole Roman Emperor Henry IV|
Rudolph (c.1025-1080) had caused trouble for Henry before. Henry had become king at the age of 6, and Rudolph took advantage of the situation and used coercion to marry Matilda, Henry's sister, and be made Duke of Swabia. He was also given administrative authority over Saxony. As Henry's brother-in-law, one might think Rudolph would be supportive, but that same family connection and the resulting position as duke made him a suitable candidate for replacing Henry years later, even though Matilda had died in 1060 and Rudolph had remarried.
The election took place in March 1077. On 25 May, the Archbishop of Mainz crowned Rudolph, who agreed to be subservient to the pope's wishes in the future. The citizens of Mainz were not supportive of this move, and in the ensuing revolt Rudolph had to flee to Saxony. Unfortunately, this cut him off from his forces and home in Swabia. Henry, still acting as king and still supported by many Germans, declared Swabia given to Frederick of Büren.
Rudolph had difficulty getting the men of Saxony to leave their homes and fight for him. But in the next few years, he made minor progress against the forces of Henry. Also, the pope excommunicated Henry again, on 7 March 1080. Things seemed to be lining up for Rudolph, but the Battle on the Elster River in October was a turning point: Rudolph sustained wounds from which he could not recover, and died the next day.
Henry then tackled the real opponent: Pope Gregory. He invaded Rome and forced Gregory out, replacing him with Pope Clement III. (Clement's appointment was, of course, irregular, and he is considered an antipope. He was pretty bad in his own right.) Rudolph's brief reign is considered that of an "anti king."
When the Protestant Reformation came, Henry IV was touted as the "first Protestant" due to his opposition to papal authority.