Tsar Alexander I was married to Louise of Baden in 1793. The match was made by his grandmother, Catherine the Great, and was not a happy one. Alexander had many affairs during his time on the throne, and many illegitimate children. His only two legimate children, both girls, died early. His heir was therefore his brother, the Grand Duke Constantine.
Constantine would often publicly disagree with his brother's policies, a habit which endeared him to the Russian people, but he never had any real political ambitions. He led a chaotic life. His marriage, another match arranged by Catherine, was even less successful than Alexander's: his wife fled back to her home in Germany after five years of wedlock. He was never a successful military leader, and was eventually sent away from the war against Napoleon due to disorderly conduct.
In 1819 Constantine became the Governor of Poland, which was then under Russian rule. Constantine became increasingly attached to his adopted land, although his rule was harsh and unpopular. Although he renounced his claim to the Russian throne in 1821, Constantine was briefly proclaimed tsar after Alexander's death in 1825. The resulting confusion led to the Decembrist Uprising, the event Tolstoy originally planned to be at the heart of War and Peace. Constantine's younger brother, Nicholas, ascended the throne and brutally crushed the rebellion.