Erik XIV of Sweden
Legend has it that King Erik XIV's last meal was a bowl of poisoned pea soup [source: Öhrström]. But we're getting ahead of ourselves. He ascended to the throne in 1560 but only ruled for eight years. The king was known to be intelligent and well-read. Erik proposed marriage to several royal women over the years (including Queen Elizabeth I) before finally marrying his mistress, a peasant woman named Karin Månsdotter in 1567 [sources: Mäkelä-Alitalo, Encyclopedia Britannica ].
Erik XIV was very ambitious and sought to expand his kingdom, an unpopular view. His half-brother Duke John also wanted to expand his territory and Erik had him imprisoned for high treason in 1563 [source: Glete]. Apparently the king began showing signs of madness and violence around this time. He ordered the murders of five nobles of the Sture family, already imprisoned for conspiracy against him. He personally stabbed Nils Svantesson Sture [sources: Cronholm, Encyclopedia Britannica].
This act proved to be too much for the other nobles, and Erik was dethroned in 1568. Duke John became ruler of Sweden, as John III. John was concerned about Erik getting out of prison, and ordered that guards should kill Erik if there was any attempt at freeing him [source: Mäkelä-Alitalo]. The pea soup, laced with arsenic, took care of that.