Who or what is the Ruach HaKodesh?

Ruach is a rich Hebrew word that means wind, breath, and spirit all at once; Hebrew does not make you choose. The Ruach HaKodesh, usually translated the Holy Spirit, is God's own breath and living presence, the same breath that gave Adam life and that writes God's instruction onto the human heart.

Here is the part to get right: the Ruach is not a separate person standing beside God, a second He. It is God's own life and presence at work in and on His people. So when Scripture shows the Spirit acting, the action is God's. He moves, He fills, He writes, by His own breath.