Tassilo III was the duke of Bavaria from 748 to 788, the last of the house of the Agilolfings. He was the son of Duke Odilo of Bavaria and Hitrud, daughter of Charles Martel.

A vassal or liege subject is a person regarded as having a mutual obligation to a lord or monarch, in the context of the feudal system in medieval Europe. While the subordinate party is called a vassal, the dominant party is called a suzerain. The rights and obligations of a vassal are called vassalage, while the rights and obligations of a suzerain are called suzerainty. The obligations of a vassal often included military support by knights in exchange for certain privileges, usually including land held as a tenant or fief. The term is also applied to similar arrangements in other feudal societies.