Riddle me this, Who am I?

Question

Feared by gods.

I share a father with some siblings but I'm the fiercest.

My two offspring dictate whether a new day begins or not.

Who am I?

Hint 1: I killed my grandpa, and I was killed by my uncle.

Answer 1

You are

Fenrir the wolf from the Norse mythology.

Feared by gods.

Fenrir was large and fierce. As a pup he was liked by the gods, but as he grew larger they began to fear him. Finally nobody but Tyr dared to handle him.

I share a father with some siblings but I'm the fiercest.

Fenrir's father was Loki. His siblings were The Midgard serpent, and the goddess Hela. Both of them were fearsome, but Fenrir was more aggressive.

My two offspring dictate whether a new day begins or not.

Fenrir had two sons; Sköll and Hati. Sköll constantly chased the sun across the sky, while Hati chased the moon, thus starting the new day.

Hint 1:

I killed my grandpa, and I was killed by my uncle.

At Ragnarok, Fenrir killed Odin, who was his adpotive his grandfather. Fenrir was later killed by Vidar, one of Odin's sons, and thus Fenrir's adoptive uncle.

Answer 2

You are

Zeus

Feared by gods.

Zeus was revered as the King of the Gods, so of course the lesser gods would fear and respect him (most of the time).

I share a father with some siblings but I'm the fiercest.

Zeus is often regarded as being more powerful than his brothers, Poseidon and Hades. This could also be a reference to Zeus being seen as enacting justice upon mortals, striking them down with bolts of lightning.

My two offspring dictate whether a new day begins or not.

This is a reference to Apollo, the god of light, and Artemis, the goddess of the night. This could also be referencing Helios and Apollo, both of whom have driven the chariot of the sun.