In his 48-year reign, the kingdom moved from one that was created from different denominational principalities and a heterogeneous agricultural country, into a constitutional state with a common identity and a well-organised management.

His father had entered the Prussian Army in 1774, then moved shortly after William's birth to the service of the Russian Empress, Catherine the Great, who appointed him Governor of Eastern Finland.

Although William's mother gave birth in 1783 to his sister Catharina Frederica, then later that year to Sophia Dorothea, and Paul in 1785, the relationship between the parents continued to deteriorate.

Catherine forced Frederick and his children to leave Russia and placed Augusta in the custody of a former royal huntsman, Reinhold Wilhelm von Pohlmann, by whom she allegedly later became pregnant.

In 1797, Duke Frederick's father married Charlotte, Princess Royal, the daughter of King George III of Great Britain.

After the War of the Second Coalition erupted and France marched under Napoleon in the spring of 1800, Frederick William, who had joined as a volunteer in the Austrian army, participated in the Battle of Hohenlinden in December 1800.

After returning to Württemberg in 1801, Frederick William and his brother Paul began liaisons with the daughters of the landscape architect, Konradin von Abel.

Elector Frederick prevented the planned marriage of his son with Therese von Abel through diplomatic interventions, though separating the two did not happen until the autumn of 1804.

On 11 September 1805 Frederick William left Paris and returned (after a visit to his grandparents, the Duke and Duchess of Brunswick-Wolfenbüttel in Brunswick) to Stuttgart, where in November he met his father for the first time in a few years.

Frederick refused to involve his son in the affairs of state, but gave him his own court headed by his friend, Ernst von Pfuel-Riepurr, who had accompanied him in his time out of the country.

From 1 January 1806, the territorial gains as a result of the German mediatization enlarged the Electorate of Württemberg and it became a kingdom upon the dissolution of the Holy Roman Empire.

On 13 August 1807 Frederick William's sister, Catherine, married Napoleon's brother Jérôme, the king of the newly created Kingdom of Westphalia.

In order to prevent Napoleon arranging a marriage for him, Frederick William sought permission from his father to marry Charlotte (later Caroline) Augusta, the daughter of the Bavarian King Maximilian I Joseph.

Frederick William ordered a retreat, but the movement quickly degenerated into a mad dash for safety across the single bridge with French cavalry in hot pursuit.

The result was a crushing Allied victory as the French corps suffered losses of 2,000 killed and wounded while losing 4,000 prisoners, 45 cannons and 100 ammunition wagons.

Annulment by Pope Pius VII, which was necessary because Charlotte was Catholic, did not take place until over a year later on 12 January 1816, shortly before the wedding of Frederick William and Catherine.

Charlotte then married on 10 November 1816, the Austrian Emperor Francis I. Frederick William and Catherine also attended the Congress of Vienna from September 1814, where diplomats drew up a new Europe following Napoleon's downfall.

After the return of Napoleon and the subsequent war in 1815, Frederick William commanded the Austrian III Corps which in one of the minor campaigns invaded France and besieged General Jean Rapp in Strasbourg.

William dismissed most of the ministers of state, made the Privy Council his government and gave new senior positions at court and in the civil service.

In April 1815, Mount Tambora erupted in the Dutch East Indies, which led to a long-term deterioration of global weather conditions.

William bought cattle and sheep from abroad for farmers to raise them in Württemberg and he was known for his Arabian stallions that formed part of the Marbach stud.

After their mother's death, Catherine's sons by her first marriage went to live with their grandfather, Peter, the-then regent and later Grand Duke of Oldenburg.

It called for a further mediatisation of small countries in Germany to the four central states of Bavaria, Saxony, Hanover and Württemberg, which together should form a counterweight to the great powers of Prussia and Austria.

In the spring of 1823, diplomatic relations were broken off, the foreign minister, Count Wintzingerode, and the Bundestag envoy, Freiherr von Wangenheim, resigned.

Seen now as a precursor of German unity under Prussia in 1871, at the time it was hoped that stronger local economies would preserve the independence of the smaller states such as Württemberg.

When Louis Philippe I abdicated and fled into exile to England, William recognised the urgency of the situation and tried the stop the revolution through concessions to the liberals and democrats.

On the morning of 30 June, in the presence of his son and successor, King Charles and his stepson Peter of Oldenburg, he was buried alongside his second wife Catherine in the Württemberg Mausoleum.

Queen Pauline and King Charles insisted Amalie of Stubenrauch left court and she moved to an estate in Tegernsee, located next to the Villa Arco, which they had acquired in 1862.

He married thrice: On 28 September 1818, one day after the king's 36th birthday, a big agricultural festival with horse races and prize-giving for outstanding cattle-breeding achievements was celebrated on the so-called Cannstatter Wasen site.

Cannstatter Volksfest and the 100th Landwirtschaftliches Hauptfest (an agricultural show)—the founding of the biggest festival in "Ländle", as the state of Baden-Württemberg is affectionately known, by King William I and his wife Katharina will be remembered in the heart of Stuttgart on the Schlossplatz square from 26 September to 3 October 2018.