Louis Ernest of Brunswick-Lüneburg-Bevern (25 September 1718, Wolfenbüttel – 12 May 1788, Eisenach) was a field-marshal in the armies of the Holy Roman Empire and the Dutch Republic, the elected Duke of Courland (1741).

A third sister was married to Ernest Frederick, Duke of Saxe-Coburg-Saalfeld and would have illustrious progeny, including Leopold I of Belgium (grandson), Queen Victoria, Albert, Prince Consort and Empress Carlota of Mexico (great-granddaughter).

Rarely were royal houses so interrelated other as in his case, and this factor was probably the main reason for his supporting the Dutch policy of neutrality during the Seven Years' War.

After the arrest of the duke of Courland, Ludwig was elected his successor on 27 June 1741 with the support of his cousin Maria Theresa of Austria.

In 1749 he entered the Dutch States Army as field marshal by request of William IV, for twenty thousand guilders per annum, although he also retained his position as an Austrian field-marshal and Protestant Generalfeldzeugmeister of the Holy Roman Empire.

Britain and Prussia asked him to command the allied armies in the Seven Years' War, but Louis Ernest refused out of respect for the Dutch Republic's neutrality.

Simultaneously, Louis Ernest began reforming the stadtholder system that had previously appointed qualified persons to the regions in reward for their loyalty.

[6][7] Earlier plans to put in place an advisory council were thus frustrated and in addition, several jealous Dutch noblemen were passed over in favour of the Duke.

He immediately observed that the princess craved joint rule, and so was starting to undermine Louis Ernest's dominant position.

[8] As early as 1771 there was talk of an attempt on his life in the Hague, but the bullet fired at him passed between his widespread legs, allegedly impacting his genitals.

The anti-stadtholder party, which gave him the nickname of "the Bulky Duke" (consistent with Frederick the Great's habit of calling him "Fat Louis") recognised the decline of the fleet, the growing importance of the Dutch States Army, the outbreak of the Fourth Anglo-Dutch War and the loss of the Barrier Treaty towns in the Austrian Netherlands, and apportioned the blame for all these to Louis Ernest first and foremost.

The disputes with Austrian Emperor Joseph II (another relative of the Duke), reopened an earlier argument over the Barrier towns, the closure of the Scheldt to shipping on Antwerp, and free trade on the Dutch East Indies.

Louis Ernest was mistrusted due to his family ties with the emperor and accused of high treason and of selling out on the fortress city of Maastricht.

Louis Ernest stayed in Eisenach from 1786, where, with the help of August Ludwig von Schlözer, he wrote his Autobiography and its sequel, his Defence.

Louis Ernest's nephew, the Duke of Brunswick-Wolfenbüttel, occupied the Dutch Republic on 13 September 1787, forcing many Patriots to flee the country.