He is made of stardust that fell from a crack in Earth into Elinder, and somehow manged to gain conciousness and create Elinder with his abilities.

Sky

He is made of stardust and therefore can take on any shape he chooses.

Stardust

Stars and sun

He is very intelligent, and can see many versions of the future

If he is sleeping, or sleepy, almost anything can be done to him. However, in order to kill him, you would need a weapon or poison created by him.

He doesn't generally interact with humans, aside from creating an occasional child. People have tried to contact him in recent years, but he hasn't responded. The only reason people believe that he's still out there is that Alex was created sixteen years ago, his only child in millennia.

Creating the net to hold Queen Rose in drained him of his power and he fell into a deep sleep. During this time, Queen Rose poisoned him with a poison made with a pinch of stardust, that nearly killed him.

He created Elinder by using objects that fell through cracks in the ceiling and turning them into deities along with him. However, when Queen Rose created herself using the stardust she found in the earth's cracks, things started to go wrong. She broke so many rules; she might have destroyed Elinder had Sky not made a very powerful net that he held her in for several years until she gave in. Unfortunately, this caused his untimely demise that nobody but Queen Rose and King Nightmare know happened. The Most Powerful Net in the Universe