In the 'kidnapped king story', the main characters include the kidnapped king. He is the center of the story, the one whose fate the whole plot revolves around. Then there are the kidnappers. They could be a group of outlaws or a foreign army. Another important set of characters are those who try to rescue the king. This could be the king's most loyal general, a brave princess who refuses to let her father be held captive, or a group of commoners who are inspired by the king's past kindness. There might also be a wise old advisor who helps the rescuers with his knowledge and experience.
The main characters in 'the kidnapped king story' are the king who is kidnapped. He is often portrayed as a just and noble leader. The kidnappers play a crucial role too. They could be motivated by greed, revenge or a thirst for power. For example, they might be a disgruntled noble who feels he has been wronged by the king. The rescuers are also key characters. They could be a valiant knight known for his strength and courage in battle, a young and intelligent page who has a special bond with the king, or a powerful mage with magical abilities to help in the rescue mission.
Typically, the king himself is a main character as he is the one kidnapped. There would also likely be the kidnappers, who could be villains like power - hungry lords or invaders. And of course, there would be the rescuers, perhaps a heroic knight or a clever wizard.