The notion of God as the King of the Universe feels odd to me because it humanizes a force that I view see as way beyond humankind. Still, personification of the Lord occurs throughout most major religions. Imagining God as our King reflects our human need to envision divinity in our image and to empower it as our ruler.
In the Gita, Lord Krishna tells us He has many forms including prayers, fire, sweets, eternity, perpetuity, destruction and the heat in the sun. Yet, further to God’s absoluteness, endlessness and everythingness, He specifically tells us that He is our King:
I am the king of the Universe.
I am its Father and Mother and Grandfather.
I am making things and taking things apart.
I am being born and dying
and I am living forever.
— The Gita, Chapter 9, Verses 17 and 18
These passages give believers freedom to shape their belief in any respectful way they can.
See The Gita, A New Translation of Hindu Sacred Scripture by Irina Gajjar.