The Sun

aka the Sun, Great Orb.

Sol is a human name for the home star of the Soly System

Doctor Who story notes
The deity worshipped by the tribal early humans in An Unearthly Child, referred to as 'Orb' may well be the Sun, or Sol. The next significant intervention of Sol in a Doctor Who story must be in The Aztecs, when the timing of a solar eclipse is crucial to the events unfolding in ancient Mexico.

In The Seeds of Death the Ice Warrior fleet is deceived into setting an irrevocable course towards the Sun.

At some point in the far future, solar flares ravage the Earth's surface such that it's inhabitants construct The Ark in Space. The Solar activity eventually subsides. Sol, along with the re-populated Earth, is eventually moved two light years by the Time Lords, causing a 'devastating fireball' which may have originated from Sol herself.

In The Ark the Earth is seen to be destroyed by the expanding star, an event also portrayed in The End Of The World.