God is “the Supreme Being; the Creator and Ruler of all that is; the Self-existent One who is perfect in power, goodness, and wisdom.” - GotQuestions
God: Creator, Judge, Redeemer
Related: Here is your God! by Alistair Begg
God is a Trinity
The God of the Bible is a Trinity. He is one eternal God existing in three distinct, simultaneous persons. There are not three Gods; there is only one God. The Bible teaches that the Father is God, Jesus (the Son) is God, and the Holy Spirit is God -- one God, three persons.
The triune nature of God is hard for the finite mind of man to fully comprehend, but it is essential to understanding who God is.