The Sun is the star at the center of our solar system. It is one of many billions of stars in the known universe, differentiated by Earthlings as Sol. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for more than 99% of the solar system's mass. Energy from the Sun -- in the form of insulation from sunlight -- supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.
It has been stated that all earth-bound life lives together "on a planet of the sun". The sun has also been known to cause sneezing, sunburns, and in certain individuals, to activate "powers and abilities far beyond those of mortal men". Big Bird has been known to greet this star with "Good Morning, Mister Sun" while the Skeksis have built an eleborate daily ritual around it. For a time, the sun refused to shine over the Kingdom of Phumph. Few have ever seen the sun come up in the west.
In Guy Smiley's "Here is Your Life" sketch on Sesame Street season 4, the Sun (performed by Jerry Nelson) pays tribute to Oak Tree, who grew thanks to the Sun's shine. Oak Tree thanks the Sun and his partner Cloud.
The character also appeared in the book Grover and the Everything in the Whole Wide World Museum.