|King of Morstaybishlia and Sultan Consort of Packilvania (Morstopackia)|
|Reign||2 April 1897 – 1 August 1917|
|Coronation||12 December 1897|
|Predecessor||Queen Rosamund II|
|Successor||King Thadeus II|
|Born||3 June 1871|
Sani Bursil Royal Palace
|Died||1 August 1917 (aged 46)|
|Spouse||Zerah Demir IV of Packilvania (m. 3 January 1897)|
|Issue||King Thadeus II|
|Father||Prince Ake of Asendavia|
|Mother||Queen Rosamund II|
Thadeus I, formally His Royal Emperor, High-King of Morstopackia, the Divine Union of the splendid Realms of Packilvania and Morstaybishlia was the King of Morstaybishlia from 2 April 1897 and the Sultan Consort of Packilvania after becoming espoused to Sultana Zerah Demir IV from the 3 January 1897 until his abrupt death on 1 August 1917. He is the only known sovereign of Morstaybishlia to marry a Paxist woman.
His father was Prince Ake Harstad of Asendavia and his mother was Queen Rosamund II. Thus, upon his ascension to the Morstaybishlian throne, the House of Harstad (which ruled over Asendavia) was briefly the Royal House of Morstaybishlia. However, due to Asendavia and Morstaybishlia fighting on different sides of the Great War, he renounced the name "Harstad" and declared the restoration of the House of Louzar (whose patrilineal line ended when Queen Florence II died and the line of the House of Visteue was established by way of Frederick III's father's surname). Technically, the relation with the original house of Louzar is tenuous given that his mother was a Visteue and his father was a Harstad, but regardless, the move was popular.
Thadeus I and Zerah Demir IV had one child, Thadeus II on the 14th of March 1901. Thadeus I died of liver failure. With the question of inheritance forced upon her by his death and the rising tide of Communism, Sultana Zemir Demir IV renounced the Morstaybishlian throne, preventing her son, Thadeus II, from claiming the Packilvanian throne. Thadeus II is the first and hitherto last person to be Sultan-King of Morstopackia.