Sun

The Sun, also known as "Sol" in Spanish, is the main and only star of the Solar System.

Formation
The Sun formed 4.57 billion years ago in a supernova cloud, from hydrogen compressing into a ball of plasma. What caused the supernova event is theorized to either be a collision of two neutron stars or a natural supernova caused by a single star. A few million years later, the Sun starts nuclear fusion with hydrogen. The Sun was likely smaller and less massive than it was today.

Present
Today, our Sun is a middle-aged yellow dwarf star. The Sun is slowly increasing in size and luminosity, which would spell disaster to the inner Solar System.

The Red Giant Phase
Due to the Sun running out of hydrogen to cause nuclear fusion, it is dying. In 5-7 billion years, the Sun will expand roughly 200 times larger, and start fusing helium. It will then "consume" Mercury, Venus, and Earth. The habitable zone will possibly reach Jupiter and Saturn. This will increase the surface temperatures of their moons, and Europa and Enceladus will have their icy surfaces melted.

White and Black Dwarf Phases
In 7-10 billion years, the Sun will die and become a white dwarf, shrinking to about the size of Earth. Over time, the remaining planets of the Solar System will cool down, due to the fact that the Sun won't produce energy in and beyond the white dwarf stage. In 10^15 (1 quadrillion or 1,000,000,000,000,000) years from now, the Sun will become a black dwarf, and cool down to a few degrees above absolute zero (273.15°Celsius).

Death
In 10^43 years from now, the Sun, along will the remaining planets will either evaporate VIA Proton Decay or be sucked into a black hole. This marks the end of our Solar System.