In The Ramayana, who are the two key players in the battle?

The two key players in the battle that defines The Ramayana are Lord Rama and the demon-king Ravana of Lanka.
The conflict between Lord Rama and Ravana is one of dharma versus adharma.  "Dharma" means living a life in accordance to the principles of duty, while "adharma" is a life that lacks such structure. The order of Lord Rama's dharma is positioned against Ravana's belief that he and his wishes are the only guiding principles that matter. This battle defines the epic.  Its resolution provides the lasting lessons to The Ramayana.
Lord Rama embodies the principles of living with the honor that comes from duty.  He willingly accepts his exile, no matter how unjust it is. He lives as an ascetic with Devi Sita and Lakshmana.  Whenever there is a threat of injustice, he does not shy away from challenging it because he sees this as his duty as a warrior.  When Ravana abducts Sita, he feels compelled to rescue her because he loves her.  However, he is also motivated because he sees it as his responsibility as a husband. Finally, Lord Rama feels that he has to challenge Ravana because the act itself is unjust and must be confronted. Lord Rama's commitment to dharma is the governing principle of his life.
Ravana believes that his desire represents the structure of the universe. He abducts Devi Sita because he covets her. He wants to add her to his collection of women to further indulge in his sensory-driven life.  His opulent display of wealth accentuates his own narcissism.   Ravana feels that he is the most powerful and most important being in the universe. He demands immediate submission from everyone because of the belief in his own greatness. Ravana does not adhere to any structure larger than himself because he feels that he is the only structure that matters.
When Lord Rama and Ravana confront one another, it is the battle between both sets of ideologies.  The Ramayana addresses how human beings should live their lives.  Do we live our lives in accordance to hedonistic self-gratification or do we recognize a duty to honor a structure larger than ourselves?  This question is answered in the battle between Lord Rama and Ravana.