The character whose actions most advance the development of the plot in "Cruel Tribute" would definitely be Theseus.
This tale puts the mythical king of Greece and prime contributor to the birth of Athens at the center of all the action. We follow his many battles against multiple villains throughout the story until he becomes a living legend, most notably after defeating the minotaur of King Minos. Theseus' struggles and conquests constitute the main driving force which propels the plot forward.
In "Cruel Tribute", King Minos of Crete had imposed a tribute of seven maidens and seven young men on Athens. This was his way of exacting revenge on the killing of his son Androgeos, who he claimed was killed by the Athenian King Aegeus. Thesues is the new found son of King Aegeus, who had volunteered to be part of the tribute to be sent to King Minos. His character's actions of fighting the Minotaur in the cave, and the subsequent following by Ariadne, the Princess of Crete all led to the development of the plot.
