The Holy Spirit is the third person of the Holy Trinity.  He reigns with Our Father and Jesus Christ.  This belief was expressed from the earliest days of the Church in the Apostles Creed.  It professes faith in the Holy Trinity — Father, Son (Jesus) and the Holy Spirit.  It states the following about the Holy Spirit:

I believe in the Holy Spirit, the holy Catholic Church and the communion of saints, …”Apostles Creed

This Creed was revised and expanded at the Council of Nicene (325 A.D.) and was called the Nicene Creed.  It is the same prayer we use today.  It states the following about the Holy Spirit:

“We believe in the Holy Spirit, the Lord, the giver of life who proceeds from the Father and Son.  With the Father and the Son he is worshiped and glorified.  He has spoken through the Prophets.”Nicene Creed

 The Holy Spirit and Jesus have a joint mission in the world.  The Catechism of the Catholic Church (CCC) states:

The One whom the Father has sent into our hearts, the Spirit of his Son, is truly God.  Consubstantial with the Father and the Son, the Spirit is inseparable from them, in both the inner life of the Trinity and his gift of love for the world.  In adoring the Holy Trinity, life-giving, consubstantial, and indivisible, the Church’s faith also professes the distinction of persons.  When the Father sends his Word, he always sends his Breath.  In their joint mission, the Son and the Holy Spirit are distinct but inseparable.  To be sure, it is Christ who is seen, the visible image of the invisible God, but it is the Spirit who reveals him. CCC 689

Jesus is Christ, “anointed,” because the Spirit is his anointing, and everything that occurs from the Incarnation on derives from this fullness.  When Christ is finally glorified, he can in turn send the Spirit from his place with the Father to those who believe in him: he communicates to them his glory, that is, the Holy Spirit who glorifies him.  From that time on, this joint mission will be manifested in the children adopted by the Father in the Body of his Son: the mission of the Spirit of adoption is to unite them to Christ and make them live in him . . .” CCC 690