Charles XII of Sweden was a king who reigned from 1697 to 1718. He became king at the young age of 15 and is best known for his military campaigns during the Great Northern War. His ambition to expand Swedish territory led to significant battles against countries like Russia, Denmark, and Poland. Despite his early successes, Charles XII faced major setbacks, particularly after the disastrous defeat at the Battle of Poltava in 1709. He spent years in exile before returning to Sweden, where he continued to pursue his military goals until his death in 1718. His reign marked the decline of Sweden as a great power in Europe.