Short answers, pulled from the story.
Henry IV was Holy Roman Emperor from 1084 to 1105, King of Germany from 1054 to 1105, and King of Italy and Burgundy from 1056 to 1105. He was born on the 11th of November 1050 and died on the 7th of August 1106. He was a Salian ruler, the son of Emperor Henry III and Agnes of Poitou.
The Walk to Canossa was a penitential journey Henry IV made in January 1077 to seek absolution from Pope Gregory VII, who had excommunicated him and released his subjects from their oaths of loyalty. Henry stood barefoot in sackcloth outside Canossa Castle for three days until Gregory, persuaded by Matilda of Tuscany, Adelaide of Savoy, and Abbot Hugh of Cluny, agreed to absolve him. Henry undertook the act to prevent Gregory from judging his case at an assembly in Augsburg controlled by his German enemies.
The Investiture Controversy was a conflict over whether secular rulers or the Church held the right to appoint bishops and abbots. Henry IV insisted on his royal prerogative to make those appointments, while Pope Gregory VII regarded lay investiture as an obstacle to Church reform. The dispute led to two excommunications of Henry, the election of an antipope, and civil war in Germany. It was only resolved in 1122 by the Concordat of Worms, negotiated between Henry's son Henry V and Pope Calixtus II.
Henry IV died in Liege on the 7th of August 1106, falling ill after being forced to abdicate and attempting to regain the throne. He died without absolution because he was excommunicated. He had requested burial at Speyer Cathedral beside his father Henry III, but his excommunicated status delayed that wish. Pope Paschal II finally permitted the burial in Speyer Cathedral on the 7th of August 1111, five years after his death.
Henry IV was seized in April 1062 in what became known as the Coup of Kaiserswerth. Archbishop Anno II of Cologne, along with Otto of Nordheim and Egbert I of Brunswick, lured the young king onto a ship on the Rhine and had it cast off, effectively removing his mother Agnes of Poitou from the regency. Agnes had lost political support due to her backing of an antipope, a failed Hungarian campaign, and favoritism toward a bishop. Henry leapt into the river to escape but was pulled out by Egbert I of Brunswick.
Otto von Bismarck declared before the Reichstag on the 14th of May 1872 that Germany would not go to Canossa, neither physically nor spiritually, during his campaign against political Catholicism. He was invoking the Gang nach Canossa as a symbol of national humiliation, reflecting the interpretation by nineteenth-century German Protestant nationalists who saw Henry IV's submission to the pope as a shameful moment for Germany.