Tsar Lunar, known as the Man in the Moon or simply "MiM", was the very first Guardian who lived on the moon and protected the dreams of all children his ship. In the movie, he is shown to be a silent, but active, observer of the transpiring events. He is the one who convinces the four Guardians that Pitch's return was a true threat, and the one who chooses Jack Frost to be the newest Guardian to aid them.
Although he never actually speaks, he can communicate through the shining of the moon's light, and is frequently spoken to by other characters. Pitch considers him an "old friend", North refers to him as "Manny", and Jack often asks him who he (Jack) is, and why he was chosen. He is only ever represented in the movie as the moon itself.
In the book
The Man in the Moon (MiM) began his life in the Golden Age, when all dreams were possible. But when his family is attacked by Pitch, The Nightmare King, MiM finds himself alone on a small moon, revolving around the planet called Earth. MiM keeps watch over the children of Earth, and vows never to let their dreams be invaded by Pitch's nightmares. MiM calls to his side, a band of heroes to serve as The Guardians.
Powers and Abilities
The Man in the Moon is the Guardian of the Children of Earth. He protects children's hope and wishes. 
The Man in the Moon is able to hear the secret fears and dreams of children via lost balloons that waft up to the moon 
The Man in the Moon's baby teeth are one of The Relics. They have a special power that let's Toothiana have the ability to see the memories within children's teeth, while also granting the ability to makes smaller copies of herself.
- "Toot toot?"
- "There are children on Earth! Children like me!"
- "Now the children of Earth will see the moon's smiling face and know they have a Nightlight to guard them forever!"
- "I wish you well."
- "I wish that you would help. When the moon's not full and bright, would you keep the children safe at night?"
- "Greetings, my valiant friends. You have faced the greatest evil of any age, and yet you never wavered. Each of you was willing to sacrifice everything for this cause. Such bravery. Such skill. Such wisdom you each have shown! For that you have my deepest thanks."
- But this fight is far from over, Pitch lives and will not stop. Can you- will you- continue the fight?"
- "Then you will need help."
- "There are four other pieces of my Moon Clipper that fell to Earth in the last Battle of the Golden Age. If these five pieces are brought together, they will become a most formidable weapon against Pitch. This first piece was my father's sword. But this is not a merely a sword for battle. Within its workings are many of the secrets of the Golden Age. Whoever wields it will need great learning, wisdom, and courage. Who among you shall take it?"
- "My valiant friends. Each night I send thousands of moonbeams down to Earth, and each night they return clear and untarnished by Pitch's dark ways."
- "It appears the world is on the cusp of a new Golden Age, a Golden Age on Earth. And it is you, my Guardians, who must guide its creation. It is a task of great daring imagination and thoughtful dreaming."
| Rise of the Guardians Wiki has|
related to The Man in the Moon.
- Nightlight was The Man in the Moon's personal Guardian.
- When the Man in the Moon was little, he wished on the Sandman's shooting star.
- In Rise of the Guardians, The Man in the Moon is never seen in person, although Pitch and the Guardians are constantly talking to him from a distance, suggesting the filmmakers intended for MiM to act as more of a more spiritual deity.