Belief in One God is called monotheism. (Mono=one.Theism=belief in God.)Tradition states that Western monotheism goes back to Abraham.
See also:
A person who believes in one God, is called a Monothiest: (Monothiesm).
Belief in only one god
They are called christians.
he believes in god and he believes that god is the one and only god
A monotheistic person believes in the existence of only one God. They worship and follow the teachings of this singular deity, often found in religions such as Christianity, Islam, and Judaism.
A Christian is someone who believes there is only one God.
a Jew. You can not believe in God and not Jesus because Jesus is God. Jesus talked about this many times.
A theist
I would call him a god, or at least someone who believes he is a god.
no, he is someone who believes in god but has no religion
God-believer. God is love.
That is someone who believes in one god but not the God of the Bible.