Who was the last ruler of the House of Habsburg-Lorraine of the Austro-Hungarian Empire?

The name Habsburg is derived from the Castle of Habsburg, or Habichtsburg (“Hawk’s Castle”), built in 1020 by Werner, bishop of Strasbourg, and his brother-in-law, Count Otto II von Habsburg. Otto II was one of the founding members of the Habsburg family. He was the son of Werner I, Count of Habsburg. Otto is presumed to be the first person to adopt the title "Graf von Habsburg" ("Graf" = Count).

The House of Habsburg was one of the most important royal houses of Europe. Although they didn't start as emperors or even kings, they eventually succeeded in their ambitions. The throne of the Holy Roman Empire was continuously occupied by the Habsburgs between 1438 and 1740 when the male line became extinct and had to continue through the marriage of Archduchess Maria Theresa Walburga Amalia Christina (13 May 1717 – 29 November 1780) with Francis I of Lorraine. Even though her husband, Francis I, was the official ruler of the Austro Hungarian Empire, Maria Theresa took charge of matters of state and the dynasty continued as the "House of Habsburg-Lorraine". Their son, Joseph II reigned between 1765-90.

Karl I of Habsburg-Lorraine (17 August 1887 – 1 April 1922) was the last Emperor of Austria, also the last King of Hungary (as IV. Károly ), and Bohemia (as Karel III ). He reigned from 21 November 1916 until 11-12 November 1918 when the Austro-Hungarian Empire was dissolved after being defeated in WWI. He never abdicated. He was beatified by Pope John Paul II in 2004.