Charles XII of Sweden

Charles XII became King of Sweden in 1697 at fifteen, inheriting a realm his enemies assumed was ripe for dismemberment. When Denmark-Norway, Saxony-Poland-Lithuania, and Russia attacked in 1700 to start the Great Northern War, he crushed a Russian army at Narva and forced Peter the Great to beg for peace - an offer he refused. By 1706, at twenty-four, he'd beaten every opponent into submission, his forces routing combined armies at Fraustadt and Holowczyn through sheer tactical brilliance. The march on Moscow began well, then shattered at Poltava in 1709 when Charles, wounded and unable to command, watched his army take catastrophic losses and surrender. He spent years exiled in the Ottoman Empire before returning to attack Norway twice in a desperate bid to knock Denmark out and refocus on Russia. A bullet at the Siege of Fredriksten in 1718 ended both campaigns and his life, with most of the Swedish Empire already under foreign occupation. He never married, never had children, and the war consumed more than half his years; his sister inherited a broken throne and a kingdom that would abandon absolute monarchy for half a century.