He was married from October 4, 1562 to Catherine Jagiellon (1526-1583), with whom he had a daughter Anna Vasa in addition to Sigismund, and from February 21, 1585 to Gunilla Johansdotter (Bielke) (1568-1597).

[2] John III was born at Stegeborg Castle on December 20, 1537, the son of Gustav I (Vasa) and his second wife, Margareta (Eriksdotter) Leijonhufvud.

[3] He was more than once the cause of his father's displeasure, especially when, as hereditary Duke of Finland Proper (since June 27, 1556), he sought to interfere in Livonian affairs behind King Gustav's back.

The break became open when John, against Erik's will, married Princess Catherine Jagiellon in Vilnius on October 4, 1562, the younger sister of Poland's King Sigismund II Augustus, with whom Erik was at war, and when the two brothers-in-law shortly after the wedding concluded an agreement according to which John would receive from the Polish king as a pledge seven permanent castles in Livonia in return for an advance of 120,000 daler.

[6] Erik considered this agreement to be in direct conflict with the Articles of Arboga - which it was - and as soon as he learned of it he demanded that John give up the Livonian castles.

[7] When the summons was not obeyed by John, he was sentenced in June 1563 by the Estates assembled in Stockholm as guilty of treason, deprived of life, property and hereditary rights to the kingdom.

John, who was unprepared for battle, was locked up in Turku Castle, defended himself there for a few weeks with 1200 men and then surrendered on August 12, 1563, in exchange for the promise of a princely prison (the Siege of Åbo).

[10] During Erik's insanity in the fall of 1567 (see the Sture Murders), John's release was secured in October 1567, after which negotiations were begun for the Duke's restoration to his rights.

John further initiated peace talks with Denmark–Norway and Lübeck to end the Northern Seven Years' War but rejected the resulting Treaties of Roskilde in which his envoys had accepted far-reaching Danish demands.

As a whole his foreign policy was affected by his connection to Poland of which country his son Sigismund III Vasa was made king in 1587.

This revolt began in July and spread so rapidly that by mid-September the army of the dukes was already outside Stockholm, whose gates were opened to them on 29 September 1568.

Erik XIV was taken prisoner, and immediately afterwards John had himself hailed as king by the city authorities and by those of the nobility and warriors who were gathered there.

Shortly after this John executed his brother's most trusted counsellor, Jöran Persson, whom he held largely responsible for his harsh treatment while in prison.

John and his wife Catherine Jagiellon had ensured that their son Sigismund received a Catholic upbringing, probably to help him acquire the Polish crown.

John responded with a political shake-up; instead of relying on the council aristocracy as before, he now sought the assistance of his brother Duke Charles, with whom he had been at bitter odds for most of his previous reign.

The reasons for this had been many, but one of the most important had been that John III, as king, had sought to apply the same principles with regard to royal rights within Charles's principality that he had so ardently opposed as duke.

In 1587 he had finally succeeded in persuading his brother to approve statutes very similar to the Articles of Arboga, which he himself had repealed in 1569, but judging from a proposal in 1590 for a new arrangement of the princely rights, he gave up the claims he had previously stubbornly maintained after the break with the high nobility.

John died in Stockholm on November 17, 1592, leaving his kingdom weakened by external and internal strife, in disorder and neglect, and for the immediate future threatened by the greatest dangers.

John's relations with the Church were initially good, although Archbishop Laurentius Petri hesitated for a long time before sanctioning the rebellion.

In domestic politics, John showed clear Catholic sympathies inspired by his Polish wife, a fact that created frictions to the Swedish clergy and nobility.

All of this can be seen as an expression of the mediating theology that John was strongly influenced by, aimed at reducing the contradictions between the various rival faiths that were tearing Europe apart at the time.

[18] This set the stage for John's promulgation of the Swedish-Latin Red Book,[9] entitled Liturgia suecanae ecclesiae catholicae & orthodoxae conformis,[19][20] which reintroduced several Catholic customs and resulted in the Liturgical Struggle, which lasted for twenty years, and attempts to negotiate with the Pope, which failed completely, partly because John's confidant in these matters, Peter Fecht, drowned during his trip to the Holy See in Rome.

John called in skilled builders, sculptors and painters from Germany and the Netherlands and also intervened himself, through his own drawings, in the prolific building activity that he provoked in so many places.

In the large circle of artists and craftsmen around John III there were some more prominent, such as the Swede Anders målare ("Anders Painter"), mostly active as a builder, Willem Boy, important both as a sculptor and architect (creator of John's tomb in Uppsala), Vadstena architects Arendt de Roy and Hans Fleming.

The castle in Uppsala (the present southern part and its western extension) was rebuilt after the fire of 1572 as a brick building with rusticated plaster and two round towers.

Vadstena Castle, like the previous one founded by Gustav I, was expanded into the Renaissance palace it still is today, although it was not completed according to the original plan until the early 17th century.

Svartsjö Palace was a curious building, with its circular arcaded courtyard and domed church on either side of an older stone house.

[24] At Kalmar Castle, where John often resided there because it was closer to Poland, the perimeter of the courtyard was completed, the floors were laid out on the same level, and in the interior the costly decoration begun under Erik XIV was continued.

Another new building was Bråborg Castle, intended as a widow's seat for Queen Gunilla, while Drottningholm (the older one, burnt down in 1661) was built on one of the islands of Lake Mälaren at the request of Catherine Jagiellon.

More purely as fortresses were Älvsborg, Gullberg, Kronoberg Castle, Kexholm, Vyborg and other places, at which significant fortification work was often undertaken, followed with interest by the king.