Short answers, pulled from the story.
Ferdinand I (the 10th of March 1503 to the 25th of July 1564) was Holy Roman Emperor from 1556, King of Bohemia, Hungary, and Croatia from 1526, and Archduke of Austria from 1521 until his death in 1564. He was the second son of Philip I of Castile and Joanna of Castile, and the younger brother of Emperor Charles V.
Ferdinand I succeeded his brother Charles V as Holy Roman Emperor when Charles abdicated in 1556. The Imperial Diet did not accept the succession until the 3rd of May 1558, and the Pope withheld recognition until 1559.
Ferdinand I's motto was Fiat iustitia, et pereat mundus, which means "Let justice be done, though the world perish".
After his brother-in-law Louis II was killed at the Battle of Mohacs on the 29th of August 1526, Ferdinand stood in the royal elections of both elective monarchies. The Bohemian Diet elected him on the 24th of October 1526, and a rump Hungarian diet at Pozsony elected him on the 17th of December 1526, with his coronation as King of Hungary on the 3rd of November 1527.
Charles V delegated authority to Ferdinand to "act and settle" disputes at the Diet of Augsburg, where he secured agreement on three principles promulgated on the 25th of September 1555. These were cuius regio eius religio, the reservatum ecclesiasticum, and the Declaratio Ferdinandei, which Ferdinand added at the last minute on his own authority.
Ferdinand fought the Ottomans over Hungary, defeating John Zapolya at Tarcal in 1527 and Szina in 1528, then surviving the Siege of Vienna in 1529 and repelling another invasion at Guns in 1532. The Treaty of Constantinople of 1533 divided Hungary between the Habsburg kingdom in the west and Zapolya's Ottoman-vassal Eastern Hungarian Kingdom.
Ferdinand I died in Vienna in 1564 and is buried in St. Vitus Cathedral in Prague. He was the last King of Germany crowned in Aachen, and his son Maximilian ascended unchallenged after his death.