The character in a work of fiction whom the reader wishes to win. The opposite of the antagonist, and usually pitted against them. If your question is more about any character, use the 'characters' tag instead.
The protagonist is the character whom the reader wishes to win. Protagonists are usually the main character and the point of view (PoV) character, though this is not always the case. Some works are about a main character who is not the protagonist nor the PoV. In this case, a different character usually serves as both, and observes the main character.
The protagonist often requires additional character development so that the reader not only likes him and wants to read about him, but sympathizes with his goal, and wants to see him complete it.
Questions with this tag should be about protagonists, including how to create/write them, and how they act or should act. If your question is targeted more to any character, consider the characters tag instead.