Matthias, Holy Roman Emperor in the context of "Bohemian Revolt"

Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae. The variety and impact of his work made Kepler one of the founders and fathers of modern astronomy, the scientific method, natural science, and modern science. He has been described as the "father of science fiction" for his novel Somnium.

Kepler was a mathematics teacher at a seminary school in Graz, where he became an associate of Prince Hans Ulrich von Eggenberg. Later he became an assistant to the astronomer Tycho Brahe in Prague, and eventually the imperial mathematician to Emperor Rudolf II and his two successors Matthias and Ferdinand II. He also taught mathematics in Linz, and was an adviser to General Wallenstein.

Rudolf II (18 July 1552 – 20 January 1612) was Holy Roman Emperor (1576–1612), King of Hungary and Croatia (as Rudolf I, 1572–1608), King of Bohemia (1575–1608/1611) and Archduke of Austria (1576–1608). He was a member of the House of Habsburg.

Rudolf's legacy has traditionally been viewed in three ways: an ineffectual ruler whose mistakes led directly to the Thirty Years' War; a great and influential patron of Northern Mannerist art; and an intellectual devotee of occult arts and learning which helped seed what would be called the Scientific Revolution. Determined to unify Christendom, he initiated the Long Turkish War (1593–1606) with the Ottoman Empire. Exhausted by war, his citizens in Hungary revolted in the Bocskai Uprising, which led to more authority being given to his brother Matthias. Under his reign, there was a policy of toleration towards Judaism.

Ferdinand II (9 July 1578 – 15 February 1637) was Holy Roman Emperor, King of Bohemia, Hungary, and Croatia from 1619 until his death in 1637. He was the son of Archduke Charles II of Inner Austria and Maria of Bavaria, who were devout Catholics. In 1590, when Ferdinand was 11 years old, they sent him to study at the Jesuits' college in Ingolstadt because they wanted to isolate him from the Lutheran nobles. A few months later, his father died, and he inherited Inner Austria–Styria, Carinthia, Carniola and smaller provinces. His cousin, Rudolf II, Holy Roman Emperor, who was the head of the Habsburg family, appointed regents to administer these lands.

Ferdinand was installed as the actual ruler of the Inner Austrian provinces in 1596 and 1597. Rudolf II also charged him with the command of the defense of Croatia, Slavonia, and southeastern Hungary against the Ottoman Empire. Ferdinand regarded the regulation of religious issues as a royal prerogative and introduced strict Counter-Reformation measures from 1598. First, he ordered the expulsion of all Protestant pastors and teachers; next, he established special commissions to restore the Catholic parishes. The Ottomans captured Nagykanizsa in Hungary in 1600, which enabled them to invade Styria. A year later, Ferdinand tried to recapture the fortress, but the action ended in November 1601 with a defeat, due to unprofessional command of his troops. During the first stage of the family feud known as the Brothers' Quarrel, Ferdinand initially supported Rudolph II's brother, Matthias, who wanted to convince the melancholic emperor to abdicate, but Matthias' concessions to the Protestants in Hungary, Austria, and Bohemia outraged Ferdinand. He planned an alliance to strengthen the position of the Catholic Church in the Holy Roman Empire, but the Catholic princes established the Catholic League without his participation in 1610.

Melchior Klesl (19 February 1552 – 18 September 1630) was an Austrian statesman and cardinal of the Roman Catholic Church during the time of the Counter-Reformation. He was minister-favourite of King and Emperor Matthias (1609-1618) and a leading advocate for peace between the empire's different confessional leagues before the Thirty Years' War.

Klesl was appointed Bishop of Vienna in 1602 and elevated to cardinal in December.

The Brothers' Quarrel (German: Bruderzwist) was a conflict between Rudolf II, Holy Roman Emperor and his brother, Matthias in the early 17th century.

Their other brothers (Maximilian III and Albert VII) and their cousins, especially Ferdinand II and Leopold V, were also deeply involved in the dispute. The family feud weakened the Habsburgs' position and enabled the estates of their realms to win widespread political and religious concessions.

Albert VII (German: Albrecht VII; 13 November 1559 – 13 July 1621) was the ruling Archduke of Austria for a few months in 1619 and, jointly with his wife, Isabella Clara Eugenia, sovereign of the Habsburg Netherlands between 1598 and 1621. Prior to this, he had been a cardinal, Archbishop of Toledo, viceroy of Portugal and Governor General of the Habsburg Netherlands. He succeeded his brother Matthias as reigning archduke of Lower and Upper Austria, but abdicated in favor of Ferdinand II the same year, making it the shortest (and often ignored) reign in Austrian history.