The first duke of Estonia was appointed in 1220 by Valdemar II after Danish conquest of Estonia during Livonian crusade

Livonian Crusade

The Livonian Crusade refers to the German and Danish conquest and colonization of medieval Livonia, the territory constituting modern Latvia and Estonia, during the Northern Crusades...

. The title was resumed by the kings of Denmark since 1269. For the period of 1266-82 during the reign of Queen Dowager Margaret Sambiria

Margaret Sambiria

Margaret Sambiria, in Danish: Margrethe Sambiria or Sambirsdatter, was the Queen consort of Christopher I of Denmark, and acted as regent for Eric V of Denmark...

 the title lady of Estonia was used.

In 1332 after Christopher II died his elder son Otto inherited the title of the duke of Estonia. Valdemar III assumed the title in 1338.

The dukes of Estonia rarely resided in Estonia. To govern the Duchy of Estonia

Danish Estonia

Danish Estonia refers to the territories of present-day Estonia that were ruled by Denmark firstly during the 13th–14th centuries and again in the 16th–17th centuries....

 the king of Denmark appointed together with royal counsellors the Lieutenant who resided in Reval.

The king of Denmark sold the duchy to Teutonic Order in 1346 but Christian I reassumed the title of duke of Estonia in 1456.

After the Livonian War

Livonian War

The Livonian War was fought for control of Old Livonia in the territory of present-day Estonia and Latvia when the Tsardom of Russia faced a varying coalition of Denmark–Norway, the Kingdom of Sweden, the Union of the Grand Duchy of Lithuania and the Kingdom of Poland.During the period 1558–1578,...

 Estonia became part of Swedish Empire

Swedish Empire

The Swedish Empire refers to the Kingdom of Sweden between 1561 and 1721 . During this time, Sweden was one of the great European powers. In Swedish, the period is called Stormaktstiden, literally meaning "the Great Power Era"...

 and the title was gained by kings of Sweden. Crown Prince Gustav Adolph

Gustavus Adolphus of Sweden

Gustav II Adolf has been widely known in English by his Latinized name Gustavus Adolphus Magnus and variously in historical writings also as Gustavus, or Gustavus the Great, or Gustav Adolph the Great,...

 was Duke of Estonia 1607-1611 before he became King, but then officially abolished all Swedish duchies in 1618.

The title was resumed by the Russian tsar

Tsar

Tsar is a title used to designate certain European Slavic monarchs or supreme rulers. As a system of government in the Tsardom of Russia and Russian Empire, it is known as Tsarist autocracy, or Tsarism...

s after the Great Northern War

Great Northern War

The Great Northern War was a conflict in which a coalition led by the Tsardom of Russia successfully contested the supremacy of the Swedish Empire in northern Central Europe and Eastern Europe. The initial leaders of the anti-Swedish alliance were Peter I the Great of Russia, Frederick IV of...

 and Treaty of Nystad

Treaty of Nystad

The Treaty of Nystad was the last peace treaty of the Great Northern War. It was concluded between the Tsardom of Russia and Swedish Empire on 30 August / 10 September 1721 in the then Swedish town of Nystad , after Sweden had settled with the other parties in Stockholm and Frederiksborg.During...

 when Estonia became part of Russian Empire

Russian Empire

The Russian Empire was a state that existed from 1721 until the Russian Revolution of 1917. It was the successor to the Tsardom of Russia and the predecessor of the Soviet Union...

. The last duke of Estonia was Nicholas II of Russia

Nicholas II of Russia

Nicholas II was the last Emperor of Russia, Grand Prince of Finland, and titular King of Poland. His official short title was Nicholas II, Emperor and Autocrat of All the Russias and he is known as Saint Nicholas the Passion-Bearer by the Russian Orthodox Church.Nicholas II ruled from 1894 until...

.