Short answers, pulled from the story.
Odoacer was the first King of Italy, proclaimed Rex Italiae by the Germanic foederati on the 4th of September 476, after the fall of the Western Roman Empire. He had previously been appointed Duke of Italy by the Byzantine Emperor Zeno in Constantinople.
The Iron Crown of Lombardy was the ceremonial crown used to invest kings of Italy from the medieval period onward. It was used to crown rulers from Odoacer's successors through the Holy Roman Emperors, and Napoleon was crowned with it at the Milan Cathedral on the 17th of March 1805. Charles V, crowned on the 24th of February 1530, was the last Holy Roman Emperor to receive the coronation.
Napoleon established a client state in northern Italy in 1805 and was crowned King of Italy on the 17th of March 1805, holding the title in personal union with his role as Emperor of the French. His kingdom did not survive his fall; it collapsed when he was deposed in April 1814.
The modern Kingdom of Italy was established on the 17th of March 1861, with Victor Emmanuel II as its first king. Unification was achieved through an alliance between the House of Savoy and the republican leader Giuseppe Garibaldi, who together overthrew the Kingdom of the Two Sicilies, followed by a popular plebiscite.
Umberto II was the last King of Italy, reigning from the 9th of May 1946 to the 12th of June 1946. He lost the throne after the 2nd of June 1946 institutional referendum, in which Italians voted to abolish the monarchy and establish a republic. He left the country on the 12th of June 1946 and died in exile on the 18th of March 1983.
The Feudal Anarchy was a period from 888 to 962 in which multiple rulers claimed the Italian kingship simultaneously after the death of Charles the Fat in January 888. During this period, a new form of the title, Rex Italicorum, meaning King of the Italians, was introduced alongside the older Rex Italiae.