Erik XIV or Eric XIV (13 December 1533 – 26 February 1577) became King of Sweden following the death of his father, Gustav I, on 29 September 1560. During a 1568 rebellion against him, Erik was incarcerated by his half-brother John III. He was formally deposed by the Riksdag on 26 January 1569. Erik was also ruler of Estonia, after it placed itself under Swedish protection in 1561.
While Erik has been regarded as intelligent and artistically skilled, as well as politically ambitious, early in his reign he showed signs of mental instability, a condition that eventually led to insanity. Some scholars claim that his illness began early during his reign, while others believe that it first manifested with the Sture murders.