Conrad Letzkau (Polish: Konrad Leczkow) (after 1350 – 1411) was a councilman and later Mayor of Danzig who, together with Arnold Hecht, was assassinated by the Teutonic Knights.

While his exact place of birth is unknown, Conrad's family came from the area of the Żuławy Gdańskie, from the village of Letzkau (then Leszkowy, hence his surname). In 1387, Letzkau came to Danzig and soon received the city's citizenship and corresponding privileges. He engaged himself in the city's commerce, amassed substantial wealth, and, in 1393, was made a councilman of the city, although official documents list him as such only later. Because of his diplomatic skills and his judicial independence, he was elected the mayor of Danzig in 1405.

This marked a part of a broader movement for city's autonomy from the control of the Teutonic Knights; previously councilmen and mayors could not be appointed without the order's approval. The growing independence caused the city to come into conflict with the newly elected Grand Master of the Order Ulrich von Jungingen who tried to interfere into the commercial activities of the city. Letzkau, along with Arnold Hecht and Peter Vorrath, was one of the initiators of a letter to the Grand Master, signed by Prussian nobility and representatives of major cities in Teutonic Prussia, complaining about the Order's tax collectors and administrators who interfered with the trade in grain and other goods in the region. Von Jungingen's policies led the leaders of Danzig to believe that the city was never going to be able to achieve the kind of independence enjoyed by other Hanseatic towns, such as the Free City of Lübeck, as long as it remained under the control of the Teutonic Order. As a result, the councilmen and the local citizens began to support the claims of the Kingdom of Poland to the region. Letzkau in particular often traveled to conventions and meetings of the representatives of Hansa towns which allowed him to compare the favorable conditions abroad with those he found in his own city under the control of the Knights.

Previously however, Letzkau took an active part in the Order's politics. In 1398, he led a united Teutonic-Hanseatic flotilla against Baltic Sea pirates, the Victual Brothers, attacked and took the island of Gotland. In 1404, while on an expedition against Danish corsairs, he was captured and imprisoned for two years in Varberg. In 1408, he served as a diplomat to the Danish Queen Margaret, in an embassy that sold the conquered island of Gotland to Denmark.

The funds obtained from the sale of Gotland were used by the Knights to arm themselves in the war against Poland-Lithuania which soon broke out. A 300-person regiment from Danzig, including Letzkau, took part in the Battle of Grunwald, fighting on the side of the Knights. The komtur leading the regiment, Johann von Schönfeld, escaped from the battlefield while most of the three hundred regular soldiers, composed mostly of Danzig's burghers and ordinary citizens, were taken captive by the Poles and Lithuanians. However, the Polish king, Jogaila, aware that the Danzigers had already been dissatisfied with the Order's rule, set all of them free, hoping to secure goodwill among them for the future.

The defeat of the Order, combined with previous anger at the Knights' economic policies, resulted in a gradual but definitive shift among the city council to a pro-Polish stance. The growing conflict between the Order and the city was acerbated when some of the wounded knights, returning from the war, were quartered in Danzig and other cities and soon were accused of robbing and abusing the citizens. Under Letzkau's orders, the city council took control of the town castle and garrisoned it with its own trusted men. The news that Thorn (modern-day Toruń) accepted the suzerainty of the King of Poland and in return received extensive civic privileges caused the city council to open negotiations with the Polish King to do the same for Danzig. The intermediary between the king and the council was the Bishop of Włocławek, Jan Kropidło. On 4 August, Letzkau and Kropidło participated in a conference with the Polish king after which the city swore an oath to the Polish King, Jagiello, who was declared "Protector of the City of Danzig", and on the next day, Jagiello bestowed the city with civic privileges similar to those previously granted to Thorn. On 7 August, the town welcomed Janusz from Tuliszkow as the king's representative and the first Starosta of Danzig.

However, as the Polish siege of Marienburg prolonged, the interim leader of the Order Heinrich von Plauen the Elder realized that the Polish–Lithuanian king did not have the means to enforce his de jure suzerainty over the rebellious towns. As a result, the Knights besieged the main part of the city of Danzig. After the Polish army abandoned the siege of Marienburg, the Danzigers and the Knights negotiated a cease fire and began negotiations for a surrender of the town. The city council sent desperate letters to Jagiello who was however unable to help. After a stormy session, the city council finally decided to swear an oath of allegiance to von Plauen, who had now been made a Master of the order.

Despite this fact, the citizens of the city continued to resent the Order's rule which manifested itself mostly through the refusal to pay taxes or otherwise support the Knights' military efforts in the war with Poland. The city refused to provide further recruits for the Order, justifying its refusal by the fact that it had also sworn a loyalty oath to the Polish king and had not yet been released from it. However, in 1411, the first Peace of Thorn was concluded, which placed Danzig under Teutonic control and Jagiello released the city from its oath.