uncaused

Existing without a perceptible cause; spontaneous.

Having no precedent cause; existing without an author; uncreated; self-existent.

Having no antecedent cause; uncreated; self-existent; eternal.

That which happens spontaneously, unintended and uninitiated.

Since all things must come from something that causes them the uncaused cause is that one thing that began the chain of existance, often identified as God.

having no cause or apparent cause