What do we call a person who believes that any ultimate reality (such as God) is unknown?

In reality, everyone should call themselves agnostic as nobody factually knows if or if not God exists. That's why believers have "faith".

Player Say what!?, that's me!

I've considered myself to be agnostic for years.

Player Say what!?, Faith is a good quality all us need .Yes I believe there's a Great powerful being that took his time to prepare this planet for life of all kinds and including human beings. And how we (human beings) are in the image of God the Creator.

Sailor Blue, None of us can't see God he is invisible to the human eyes, we see the creation around us,it just didn't happen to be. Some one made it. We can't see the wind, but it exists.A house didn't construct itself , someone made it! I believe there is an all powerful being,because of the evidence around us.

also atheist