Pope Gregory and King Henry IV king were two men living in 1073. Before the two were given their positions there had been conflict between the pope and king because of power. Pope Gregory had strong ideas about the power of the Pope. The two were very strong willed which could be a problem later on.
Later on the Pope declared new rules that consisted of him having the power to appoint bishops, and the ability to remove an emperor from the throne. King Henry did not like this because they were an attack on his rights. This made a clash between the two men.
King Henry was really mad, so he did not follow the popes rules. He elected his own Bishop. Gregory then elected another rival Bishop which cause more rivalry.
How could he do such a thing?
I have to get him back!
The two men kept fighting and the people of Europe took sides. The King tried to remove Gregory from being the pope, but Gregory excommunicated Henry. Also the Pope freed all of King Henrys subjects.
You cannot do that! I am banishing you from the church, and I never want to see your face there again!
I do not want you to be Pope anymore, you are removed!
King Henry had to wait outside the castle in the snow for three days before the Pope would see him. The pope had forgiven him, and once they talked again Henry was still fighting. He sent an army to take the Popes job from him.
The fighting between the Pope and King lasted until after King Henry died. Finally they came to an agreement called the Concordat of Worms. Even though this existed the fighting between Popes and Kings lasted a long time after that.