God has three persons, first, second, and third... otherwise known as Father, Son, and Holy Spirit. We are made in God's image; we have three persons; ever talk to yourself? Before he breathed out all those angels he was all those angels; before he breathed into Adam's nostrils the breath of Life, he was the breath of Life, before he breathed on the disciples at Pentecost and told them to receive the Holy Ghost, he was the Holy Ghost.

#1 commandment: the lord your God is one God.

The Holy Spirit is just God... It's a personality thing.