Merlin is a sorcerer who helps Uther marry Igraine by arranging for Arthur to grow up away from the royal court. He has magical abilities like seeing the future and making people do what he wants. But his powers are not unlimited, and he's not perfect. Eventually, he gives in to his desires, which causes his downfall and death.
Merlin's main job is to use his magic to help people, like Uther, but sometimes he gets caught up in his own wants. This leads to problems, especially when he can't control his desires. Despite his powers, Merlin is still human and makes mistakes.