thumb|Maximilian Kaller
thumb|Bust of Kaller in [[Frombork's Archcathedral Basilica of the Assumption of the Blessed Virgin Mary and St. Andrew, Frombork.]]
Maximilian Kaller (10 October 1880 – 7 July 1947) was Roman Catholic Bishop of Ermland () in East Prussia from 1930 to 1947. However, de facto expelled from mid-August 1945, he was a special bishop for the homeland-expellees until his death.
Early life
Kaller was born in Beuthen (Bytom), Prussian Silesia, into a merchant family, the second of eight children. With the population of Beuthen being of German and Polish ethnicity he grew up bilingual in German and Polish. He graduated from the Gymnasium in 1899 with Abitur and started theological studies in Breslau (today's Wrocław) at the episcopal see of his then home Prince-Bishopric of Breslau. There he was consecrated a priest in 1903.
He was the chaplain in the parish of Groß Strehlitz (today's Strzelce Opolskie) in the Breslau diocese. From 1917, he was the priest at Berlin's second oldest Catholic Church, Saint Michael's Garrison Church. Kaller's jurisdiction comprised Catholic parishes of the dioceses of Chełmno and of Gniezno-Poznań, which had been separated from their episcopal sees by the new Polish border in 1918 and 1920, respectively. Franz Hartz succeeded Kaller as Prelate of Schneidemühl.
thumb|Grave of Maximilian Kaller – with bishop Adolf Kindermann in [[Königstein im Taunus]]
From 1925, Ermland diocese comprised all of the Prussian Province of East Prussia in its borders of 1938. In the year of Kaller's investiture, his diocese, which had turned exempt in 1566 when its original metropolitan Archbishopric of Riga, had become Lutheran and was de jure dissolved, became again suffragan to an archdiocese. Ermland diocese, together with the new Berlin diocese and Schneidemühl prelature joined the new Eastern German Ecclesiastical Province () under the newly elevated Metropolitan Archbishop Adolf Bertram of Breslau.
In 1932, Kaller consecrated the new diocesan seminary for priests in Braunsberg in East Prussia (today's Braniewo). Under his jurisdiction, Ermland diocese issued a new diocesan hymnal and a diocesan ritual (cf. Rituale Romanum) in Latin and the three native languages of the diocesan parishioners (German, Lithuanian and Polish).
After World War II
After World War II, most Germans were expelled to Allied-occupied Germany, including Marquardt who had to leave in July. Frauenburg's cathedral chapter then elected the aged Canon Johannes (Jan) Hanowski, a German of Polish ethnicity and long-term archpriest of Allenstein (today's Olsztyn), as capitular vicar, i.e. provisional head of the see, on 28 July 1945.
Kaller, who had been stranded by the end of the war in Halle upon Saale, made his -long way back to his see and arrived on one of the first nights of August 1945 in Allenstein/Olsztyn, taking on the jurisdiction from Hanowski. He started to develop new plans for his diocese especially aiming at overcoming the nationalist antagonism between Catholics of the German and Polish languages, reshaping the diocese in the spirit of German-Polish reconciliation.
Kaller further appointed an ethnic Pole as new cathedral provost, since his predecessor provost, Franz Xaver Sander (also official), and five more fellow cathedral canons had been killed by the invading Soviets. (The other killed canons were Andreas Hinzmann, Dr. Franz Heyduschka, Dr. Wladislaus Switalski, Anton Krause and Dr. Bruno Gross.) Addressing the Polish authorities in the annexed area of his diocese, Kaller declared that he wanted to continue his episcopate within Poland, but officials said it was for neither him nor them, but Warsaw to decide that. Afterwards, in a private conversation, Hlond urged Kaller to resign which he did for the jurisdiction in the Polish-occupied diocesan area, but retained the office of Bishop of Ermland, The Holy See later confirmed him and thereafter Kather represented Ermland diocese in the Fulda Conference of Bishops until his death.