The sun

The Sun, know as Helios in Greek and Sol in Latin is the Star at the center of Earth's solar system and one of, if not the greatest source of natural energy on Earth.

Of course to Goku, the Sun serves almost as a secondary ally, whose help he can call on when times get tough, and he needs help to beat someone up real bad.

What is the point of the Sun?
If you were to ask a scientist, they would tell you that the Sun privides essential energy to the planet, sunlight providing nutrients and warmth that keeps the Earth's ecosystem stable and functional. However, to Goku, the Sun is a plot device that can be used to draw energy for a real big Kamaya-Maya! Or as a place to dispose of the body of his enemies in a torturous and grotesque fashiin which essentially involves burning them alive. But then again, it was Cooler.