Jesus Christ is fully God and fully man, united in something called a hypostatic union. Some have called into doubt just how much He knew about His divinity at different points in His life on Earth, but it is clear that Jesus knew from earliest times that He is God. He knew that He should be about His father’s business in the temple, He proclaimed Himself as the Son of God, not as an adopted sonship, but as a natural son.
His opponents used the very same statements to condemn Him, stating that He had called Himself God, and when they gave Him an opportunity to clarify what He meant, Jesus did not deny that He is God. Heresies arose about this doctrine from both sides, with some like the Arians denying Christ’s divinity, and the Docetists attacking His humanity. The Church has made statements several times refuting these errors.