Catherine the Jagiellonian of Poland (Polish: Katarzyna Jagiellonka; Lithuanian: Kotryna Jogailaitė; Finnish: Katariina Jagellonica; Swedish: Katarina Jagellonica av Polen; 1 November 1526 – 16 September 1583) was Duchess of Finland (1562–83), Queen Consort of Sweden (1569–83), Grand Princess of Finland (1581–83) and heir to her mother's claim to the title of King of Jerusalem.

She was born the youngest daughter of King Zygmunt I the Old of the Polish-Lithuanian Commonwealth and Bona Sforza. Catherine became the wife of King John III of Sweden and mother of the future King Sigismund III Vasa of the Polish-Lithuanian Commonwealth. Tsar Ivan IV of Russia was among her suitors.

On 4 October 1562, Catherine was married in the Lower Castle of Vilnius, Lithuania, to Duke John of Finland, later King John III of Sweden, the second son of King Gustav I of Sweden and half-brother of the then-reigning King Eric XIV. John had not received his brother's permission for the marriage and there were already tensions between them, since John pursued an independent foreign policy. The newlyweds set up house in Turku Castle in Turku, Finland. Duke John's dealings in Livonia caused King Eric XIV to declare war on his brother. Eric sent 10,000 men to besiege the castle.

On 12 August 1563 the castle capitulated; Catherine and her husband were taken to Sweden and imprisoned in Gripsholm Castle.

Catherine's unsuccessful suitor Tsar Ivan was in negotiations with Eric in hopes of separating her from John and sending her to marry him in Russia. This caused alarm with Catherine and her relations. In popular opinion, this discussion was one of the reasons for the Swedish people's growing dissatisfaction with the increasingly insane Eric. King Eric agreed to hand over Catherine to Ivan, but the Swedish king was deposed before Catherine could be sent away. As his brother John succeeded him, the problem disappeared.

During her incarceration, Catherine gave birth first to her eldest daughter Isabella of Finland in 1564 (died 1566), then to her son Sigismund in 1566, and finally her youngest child Anna Vasa of Sweden on 17 May 1568.

Catherine and John were released in 1568. In 1569, she was crowned Queen of Sweden after her husband deposed Eric and usurped his throne.

Queen Catherine had political influence and did much to influence her husband on behalf of the cause of Catholicism and the Counter-Reformation, just as her successor as queen, her husband's later wife Gunilla Bielke, would try to influence him on behalf of Protestantism. John launched a new church order called "The Red Book".

This was a form of mix between Protestantism and Catholicism that reintroduced numerous Catholic customs in the ceremonial life of the Swedish church. It even used Latin, which aroused a great deal of opposition. Catherine had her own Catholic staff, among them several Catholic monks and priests, which shocked the Protestants.

In 1572, she contacted Cardinal Hosius about re-Catholicising Sweden. In 1573, the son of the deposed King Eric and Karin Månsdotter were sent to the Jesuits in Poland. In 1575, a ban left over from the Reformation period to accept new novices in the remaining Catholic convents in Sweden was lifted.

In 1576, she sent her son to be educated by the Jesuits in Braunsberg. From Rome came the Norwegian Jesuit Laurentius Nicolai, whom she housed in an old Franciscan monastery that had been closed during the Reformation.

She allowed Nicolai to open a Catholic school there, but the Protestants stormed the school, and it was closed in 1583. A new shrine was made for the relics of King Eric the Saint in the cathedral of Uppsala. Queen Catherine strongly supported the old Vadstena Abbey, where the last nuns still lived, and often visited it. The first version of the later famous royal palace of Drottningholm (The Queen's Islet) was founded for and named after her. In her final years, Catherine suffered from gout.

She died in Stockholm on 16 September 1583 and was buried in the royal crypt of the Uppsala Cathedral.

Legacy

The infusion of Polish blood into the Swedish royal lineage that begun with Catherine would cause considerable strife after her death in the context of the ongoing European wars of religion.

Her son Sigismund inherited the thrones of both the Polish-Lithuanian Commonwealth (in 1587) and Sweden (in 1592), but ruled the latter only seven years before being deposed in 1599. Sigismund and his descendants, as Catholic kings, would continue to lay claim to de facto Protestant Sweden over the following century.

The succession dispute contributed to the outbreak of several destructive wars until a massive Swedish invasion in the 1650s (known as the Deluge) nearly broke up the Polish-Lithuanian Commonwealth. Polish claims to the Swedish throne were finally relinquished in the 1660 Treaty of Oliva.

The image of Catherine Jagellon enjoyed a resurgence in 19th and 20th century Finnish culture and art. John and Catherine were the only Swedish monarchs to reside in the Finnish part of the Swedish realm for any length of time, and their alleged fondness for the land inspired Finnish nationalists. The religious issues that made Catherine unpopular with her contemporaries were by then long obsolete, and it has instead become traditional to depict her as a compassionate and loyal queen.