Question: Leopold I, was Holy Roman Emperor, King of Hungary, Croatia, and Bohemia, he's the second son of which emperor?
Context: Ferdinand III (13 July 1608 – 2 April 1657) was Holy Roman Emperor from 15 February 1637 until his death, as well as King of Hungary and Croatia, King of Bohemia and Archduke of Austria.  He was the last emperor to have real power over the Holy Roman Empire. Archduchess Maria of Austria (21 June 1528 – 26 February 1603) was Holy Roman Empress and queen consort of Bohemia and Hungary as the spouse of Maximilian II, Holy Roman Emperor and King of Bohemia and Hungary.  She served as regent of Spain in the absence of her father Emperor Charles V from 1548 until 1551, and in the absence of her brother Philip II, from 1558 to 1561. The monarchs of Prussia were members of the House of Hohenzollern who were the hereditary rulers of the former German state of Prussia from its founding in 1525 as the Duchy of Prussia.  The Duchy had evolved out of the Teutonic Order, a Roman Catholic crusader state and theocracy located along the eastern coast of the Baltic Sea.  The Teutonic Knights were under the leadership of a Grand Master, the last of whom, Albert, converted to Protestantism and secularized the lands, which then became the Duchy of Prussia.  The Duchy was initially a vassal of the Kingdom of Poland, as a result of the terms of the Prussian Homage whereby Albert was granted the Duchy as part of the terms of peace following the Prussian War.  When the main line of Prussian Hohenzollerns died out in 1618, the Duchy passed to a different branch of the family, who also reigned as Electors of Brandenburg in the Holy Roman Empire.  While still nominally two different territories, Prussia under the suzerainty of Poland and Brandenburg under the suzerainty of the Holy Roman Empire, the two states are known together historiographically as Brandenburg-Prussia.  Following the Second Northern War, a series of treaties freed the Duchy of Prussia from any vassalage to any other state, making it a fully sovereign Duchy in its own right.  This complex situation (where the Hohenzollern ruler of the independent Duchy of Prussia was also a subject of the Holy Roman Emperor as Elector of Brandenburg) laid the eventual groundwork for the establishment of the Kingdom of Prussia in 1701.  For diplomatic reasons, the rulers of the state were known as the King in Prussia from 1701 to 1772; largely because they still owed fealty to the Emperor as Electors of Brandenburg, the "King in Prussia" title (as opposed to "King of Prussia") avoided offending the Emperor.  As the Prussian state grew through several wars and diplomatic moves throughout the 18th century, it became apparent that Prussia had become a Great Power that did not need to submit meekly to the Holy Roman Empire.  By 1772, the pretense was dropped, and the style "King of Prussia" was adopted.  Thus it remained until 1871, when in the aftermath of the Franco-Prussian War, the King of Prussia Wilhelm I was crowned German Emperor.  From that point forward, though the Kingdom of Prussia retained its status as a constituent state of the German Empire, all remaining Kings of Prussia also served as German Emperor, and that title took precedence. Maximilian II (31 July 1527 – 12 October 1576), a member of the Austrian House of Habsburg, was Holy Roman Emperor from 1564 until his death.  He was crowned King of Bohemia in Prague on 14 May 1562 and elected King of Germany (King of the Romans) on 24 November 1562.  On 8 September 1563 he was crowned King of Hungary and Croatia in the Hungarian capital Pressburg (Pozsony in Hungarian; now Bratislava, Slovakia).  On 25 July 1564 he succeeded his father Ferdinand I as ruler of the Holy Roman Empire. Gerasim Zelić (Serbian: Герасим Зелић ; 1752–1828) was a renowned Serbian Orthodox Church archimandrite, traveller and writer (a contemporary and compatriot of Dositej Obradović).  His chief work is "Žitije" (Lives), in three volumes.  They are memoirs of his travels throughout western Europe, Russia and Asia Minor from the latter half of the 18th century to the first decade of the 19th century and the famous personalities (Napoleon, Prince Eugène, Viceroy of Naples, Joseph II, Holy Roman Emperor, Leopold II, Holy Roman Emperor, Francis II, Holy Roman Emperor, Semyon Zorich, Catherine the Great, Alexander I of Russia, Stanisław August Poniatowski, Dositej Obradović) he met.  He had valuable original notes on people, religions, manners, customs, trade, etc. Leopold II (Peter Leopold Josef Anton Joachim Pius Gotthard; 5 May 1747 1 March 1792) was Holy Roman Emperor and King of Hungary and Bohemia from 1790 to 1792, Archduke of Austria and Grand Duke of Tuscany from 1765 to 1790.  He was a son of Emperor Francis I and his wife, Empress Maria Theresa, thus the brother of Marie Antoinette.  Leopold was a moderate proponent of enlightened absolutism. Otto Heinrich Fugger, Count of Kirchberg and Weissenhorn (1592–1644) was promoted to be a Knight of the Order of the Golden Fleece in 1628.  He was the son of Christoph Fugger von Glött, deceased 1615, the grandson of Johann Fugger, deceased 1598, the great grandson of very wealthy Augsburg city International businessman and banker Anton Fugger (1493–1560).  The 16th century Fugger's, descendents of a German businessmen family tracked down to the 14th century, were the Imperial bankers with King Charles I of Imperial Spain, also Holy Roman Emperor as Charles V (1500–1558), and his brother, also Holy Roman Emperor, Ferdinand I of Habsburg (1503–1564), king of Hungary and Bohemia from 1526, emperor from 1556 by abdication of his brother Charles. Leopold I (name in full: "Leopold Ignaz Joseph Balthasar Felician"; Hungarian: "I. Lipót" ; 9 June 1640 – 5 May 1705) was Holy Roman Emperor, King of Hungary, Croatia, and Bohemia.  The second son of Ferdinand III, Holy Roman Emperor, by his first wife, Maria Anna of Spain, Leopold became heir apparent in 1654 by the death of his elder brother Ferdinand IV.  Elected in 1658, Leopold ruled the Holy Roman Empire until his death in 1705. Ferdinand I (Spanish: "Fernando I" ) (10 March 1503 – 25 July 1564) was Holy Roman Emperor from 1558, king of Bohemia and Hungary from 1526, and king of Croatia from 1527 until his death.  Before his accession, he ruled the Austrian hereditary lands of the Habsburgs in the name of his elder brother, Charles V, Holy Roman Emperor.  Also, he often served as Charles' representative in Germany and developed useful relationships with German princes. Archduke Alexander Leopold of Austria (Alexander Leopold Johann Joseph; Hungarian: "Sándor Lipót" ; 14 August 1772 – 12 July 1795) was Palatine of Hungary, appointed during the reign of his father, Holy Roman Emperor Leopold II, and serving into the reign of his elder brother, Holy Roman Emperor Francis II.
Answer: Ferdinand III, Holy Roman Emperor