Assan is the Sultan's brother, ruler of a distant land.
Assan tricks the Sultan and his family into coming to his palace. He attempts to imprison the Prince, but he escapes, and goes after Assan.
It turns out that they had a pact that the Princess would marry Assan's son Rugnor. He attempts to kill the Prince, but the Sultan blocks the blow, and is killed. Assan flees, and his fate is unknown after this.