Excerpts from Books and Wikipedia
"Ferdinand I (…) was Holy Roman Emperor from 1556 . . . until his death in 1564. Before his accession, he ruled the Austrian hereditary lands of the Habsburgs in the name of his elder brother, Charles V, Holy Roman Emperor. . . . The key events during his reign were the contest with the Ottoman Empire, which in the 1520s began a great advance into Central Europe, and the Protestant Reformation, which resulted in several wars of religion. Ferdinand was able to defend his realm and make it somewhat more cohesive, but he could not conquer the major part of Hungary. His flexible approach to Imperial problems, mainly religious, finally brought more result than the more confrontational attitude of his brother." [Wikipedia] "Charles V’s inheritance of the crowns of four major dynasties, Castile, Aragon, Burgundy, and Austria, the later acquisitions by his house of the crowns of Bohemia, Hungary, Portugal, and, for a short time, even of England, and the coincidence of these dynastic events with the Spanish conquest and exploitation of the New World—these provided the house of Habsburg with a wealth of resources that no other European power could match."