Duke in Bavaria (German: Herzog in Bayern) was a title used among others since 1506, when primogeniture was established, by all members of the House of Wittelsbach, with the exception of the Duke of Bavaria which began to be a unique position. So reads for instance the full title of the late 16th century's Charles I, Count Palatine of Zweibrücken-Birkenfeld and patriarch of the House of Palatinate-Birkenfeld: "Count Palatine by Rhine, Duke in Bavaria, Count to Veldenz and Sponheim". The title grew in importance as Wilhelm, Count Palatine of Zweibrücken-Birkenfeld-Gelnhausen began to use it, in the early 19th century, as his primary titleDuke Wilhelm in Bavaria. This choice has also had effect for his descendants.
On 16 February 1799, the head of the House of Wittelsbach Charles Theodore of Bavaria died without legitimate issue. Wittelsbach had been the ruling house of Bavaria since 1180 with the title of a Duke of Bavaria, and the higher title of an Elector of the Holy Roman Empire since 1623. As after the Landshut War of Succession primogeniture was established, there could only be one Duke of Bavaria anymore, resulting in the unprecedented decision to create a title of Duke in Bavaria for the rest of the family, which all members of the House took for themselves, even the older Palatine branch – the other major Wittelsbach possession. Reversely, all Wittelsbachs were also Counts Palatine by Rhine. After the death of Charles Theodore, who had unified Bavaria with the Palatinate and the other major possessions of Jülich and Berg in his person, two cadet branches were surviving: one headed by Maximilian I Joseph, Count Palatine of Zweibrücken, the other by William, Count Palatine of Gelnhausen, and both Zweibrücken and Gelnhausen were occupied by the French, which might explain why the custom was abandoned to name cadet branches by the title of their cadet possessions no matter how small.
They both agreed in the House Treaty of Ansbach that the Wittelsbach inheritances should be indivisible further on. Maximilian Joseph, being from the senior branch, inherited Charles Theodor's title of Elector of Bavaria, while William, his brother-in-law in addition to rather distant a relative, was compensated with the title of Duke in Bavaria. As head of a specific family branch, it is possible since to speak somewhat paradoxically of The Duke in Bavaria. When Wittelsbach became a Royal House, the Dukes in Bavaria were lifted to the dignity of a Royal Highness. Then if not earlier, the title of Duke in Bavaria came into formal disuse by the Royal branch, who were quite content to be Princes of Bavaria. It should be kept in mind that even if we commonly speak of a Royal and a Ducal branch of the House, it was clear that the Dukes as well were of royal rank, and to make things more complicated, the head of the royal branch is now again called the Duke: the Duke of Bavaria, of course. Among the notable members of the Ducal branch were Duke Max who, a talented Zither player and composer himself, ranks among the most important promoters of Bavarian folk-music; his daughters Empress Elisabeth of Austria, Queen of Hungary and Queen Maria of the Two Sicilies, his granddaughter Queen Elisabeth of Belgium; and in more recent times Sophie, Hereditary Princess of Liechtenstein.
In 1965 there were only two male members of the family, Duke Ludwig Wilhelm and his cousin Duke Luitpold; both were elderly and had no children. On 18 March 1965 Duke Ludwig Wilhelm adopted Prince Max of Bavaria, the second son of Albrecht, Duke of Bavaria and the grandson of Ludwig Wilhelm's sister Marie Gabrielle. From this point onwards Max has used the surname "Herzog in Bayern" in place of the surname "Prinz von Bayern". Max has five daughters, including the Sophie mentioned already, all of whom were born with the surname "Herzogin in Bayern".
Wilhelm, the first Duke in Bavaria, was descended from the line of Palatinate-Zweibrücken-Birkenfeld-Gelnhausen. His ancestors were:
The members of the family used the title Duke or Duchess in Bavaria, with the style of Royal Highness. If we take 1799 as the beginning of somewhat a House of its own, the heads of this house were:
In 1813 Duke Wilhelm in Bavaria acquired a former monastery after its secularisation, the Franconian Banz Abbey. His grandson Duke Maximilian Joseph in Bavaria purchased Possenhofen Castle on Lake Starnberg which became his major residence and where his children, notably the later Empress Elisabeth of Austria, Queen of Hungary ("Sisi"), were brought up. In 1838 he acquired Unterwittelsbach Castle (today housing a "Sisi" museum) near the site of Burg Wittelsbach, the ancestral seat of the House of Wittelsbach. His wife, Princess Ludovika of Bavaria, daughter of King Maximilian I Joseph of Bavaria, inherited the Upper Bavarian Tegernsee Abbey, purchased in 1817 by king Maximilian I Joseph, together with the nearby bath house at Kreuth.
Luitpold Emanuel Ludwig Maria, Duke in Bavaria (1890-1973), the last issue of the in Bavaria junior branch, sold Possenhofen and Schloss Biederstein in Munich in order to finance his late romantic Schloss Ringberg, which he eventually left as inheritance to the Max Planck Society. His cousin Duke Ludwig Wilhelm in Bavaria, also childless, in 1965 adopted a grandson of his sister Marie Gabrielle, who had married Rupprecht, Crown Prince of Bavaria, Prince Max Emanuel of Bavaria of the senior royal branch, who inherited the estates at Banz, Tegernsee and Kreuth from his uncle and, from his father's side, Wildenwart Castle near Frasdorf, which had been purchased by Francis V, Duke of Modena in 1862 who left it to his niece, the Bavarian Queen Maria Theresa.